General Chemistry MCAT Flashcards
What is the charge of a proton?
• (1.6 × 10− 19 C)=charge of a proton
What are the three isotopes of hydrogen?
protium, deuterium, and tritium
Desccribe the energy levels in electrons in the various shells?
• The electrons closer to the nucleus are at lower (electric potential) energy levels, while those that are in the outer regions (or shells) have higher energy
How much is 1 atomic mass unit worth?
• 1amu=1.66 × 10− 24 grams
How big is 1 mole?
• 1mol=Avogadro’s number: 6.022 × 1023
What is the energy and frequency equation?
• E=hf= J=(Js)(1/s). h=6.626x10-34 Planck’s constant
What did Bohr describe as his model of the atom?
- Bohr’s model- Bohr assumed that the hydrogen atom consisted of a central proton around which an electron traveled in a circular orbit and that the centripetal force acting on the electron as it revolved around the nucleus was the electrical force between the positively charged proton and the negatively charged electron.
- The Bohr model of the atom consists of a dense, positively charged nucleus surrounded by electrons revolving around the nucleus in defined pathways of distinct energy levels called orbits
which has applications of o The energy difference between energy levels is called a quantum
• The energy of an electron is quantized, which means that there is not an infinite range of energy levels available to an electron; electrons can exist only at certain energy levels, and the energy of an electron increases the farther it is from the nucleus with energy increasing the farther out from the nucleus it is located.
What is the angular momentum equation?
• angular momentum=L=mvr kintetic energy=KE=1/2mv2
What is the mass of an electronand its significance?
• The mass of an electron is approximately 1/1836 with these subatomic particles mass so small, the electrostatic force of attraction between the unlike charges of the proton and electron are far greater than the gravitational force of attraction based on their respective masses
What is the rhydberg constant?
RH= rhydberg constant=2.18x10-18 J/electron
what is the speed of light?
• speed of light= c= 3x108 m/s
What are the Balmer and lyman series?
- n > 2 energy level to the n = 2 energy level is known, the Balmer series and includes four wavelengths in the visible region
- n > 1 to n = 1 (that is, the emissions of photons from the electron falling from the higher energy levels to the ground state) is called the Lyman series, which includes larger energy transitions and therefore shorter photon wavelengths in the UV region of the electromagnetic spectrum.
What is the heisenberg uncertainty principle?
• Heisenberg uncertainty principle: It is impossible to simultaneously determine, with perfect accuracy, the momentum and the position of an electron. If we want to assess the position of an electron, the electron has to stop (thereby changing its momentum); if we want to assess its momentum, the electron has to be moving (thereby changing its position).
What is the pauli exclusion principle?
• Pauli exclusion principle, no two electrons in a given atom can possess the same set of four quantum numbers
What is the quantum number
• N=The larger the integer value of n, the higher the energy level and radius of the electron’s orbit(al). Within each shell of some n value, there is a capacity to hold a certain number of electrons two per orbital equal to 2n2, and the capacity to hold electrons increases as the n value increases. The difference in energy between two shells decreases as the distance from the nucleus increases
What is the azimuthal number?
- l= azimuthal (angular momentum) quantum number and is designated by the letter l. The second quantum number refers to the shape and number of subshells within a given principal energy level (shell)
- The range of possible values for l is 0 to (n− 1). 1st orbital has n=1 and l=0. N=2 & l=0=s, 1=p…
- The maximum number of electrons that can exist within a given subshell is equal to 4l + 2. For any value of l, there will be 2l + 1 possible values for ml. For any n, this produces n2 possible values of ml (i.e., n2 orbitals). the 4s subshell will have a lower energy than the 3d subshell.
- l = 0 → s
- l = 1 → p
- l = 2 → d
What is the magnetic quantum number?
What is the designation between paramagnetic and diamagnetic?
- magnetic quantum number and is designated ml. The magnetic quantum number specifies the particular orbital within a subshell where an electron is highly likely to be found at a given moment in time. Each orbital can hold a maximum of two electrons. − l and +l, including 0
- Remember that paramagnetic means that a magnetic field will cause parallel spins in unpaired electrons and therefore cause an attraction. Materials consisting of atoms that have all paired electrons will be slightly repelled by a magnetic field and are said to be diamagnetic.
What is the spin quantum number?
• spin quantum number and is denoted by ms. Whenever two electrons are in the same orbital, they must have opposite or parallel spins. Hund’s rule, which states that within a given subshell, orbitals are filled such that there are a maximum number of half-filled orbitals with parallel spins
What are the designation of the periodic table?
• periods (rows) and groups (columns), also known as families.
What is the general trend of the positivity of a nucleus in the periodic table?
• As the “ positivity” of the nucleus increases, the electrons surrounding the nucleus, including those in the valence shell, experience a stronger electrostatic pull toward the center. This causes the electron cloud, the “ outer boundary” defined by the valence shell electrons, to move closer and bind more tightly to the nucleus. This electrostatic attraction between the valence shell electrons and the nucleus is known as the effective nuclear charge(Zeff), a measure of the net positive charge experienced by the outermost electrons. For elements in the same period, Zeff increases from left to right.
What is the general trend of the valence electrons in the periodic table?
• Valence electrons are increasingly separated from nucleus by greater number of filled principal energy levels, which can also be called “ inner shells.” With a reduction in the electrostatic attraction between the valence electrons and the positively charged nucleus. These outermost electrons are held less tightly as the principal quantum number increases. As you go down a group, the increase in the shielding effect of the additional insulating layer of inner shell electrons negates the increase in the positivity of the nucleus (the nuclear charge). So, the Zeff is more or less constant among the elements within a given group. In spite of this, the valence electrons are held less tightly to the nucleus as you move down a group due to the increased separation between them.
What is the general trend of the atomic radius in the periodic table?
• Atomic radius- Because the electrons are being added only to the outermost shell and the number of inner-shell electrons remains constant, the increasing positive charge of the nucleus holds the outer electrons more closely and more tightly. The Zeff increases left to right across a period, and as a result, atomic radius decreases from left to right across a period. As we move down a group, the increasing principal quantum number implies that the valence electrons will be found farther away from the nucleus because the number of inner shells is increasing, separating the valence shell from the nucleus. Although the Zeff remains essentially constant, the atomic radius increases in a group from top to bottom. within each group, the largest atom will be at the bottom, and within each period, the largest atom will be in Group IA (Group 1)
What is the general trend of the ionization energy in the periodic table?
energy required to remove an electron from a gaseous atom or ion. Removing an electron from an atom always requires an input of energy, which makes it an endothermic process. The greater the atom’s Zeff or the closer the valence electrons are to the nucleus, the more tightly they are bound to the atom. This makes it more difficult to remove one or more electrons, so the ionization energy increases. Thus, ionization energy increases from left to right across a period and decreases in a group from top to bottom. subsequent removal of a second or third electron requires increasing amounts of energy, because the removal of more than one electron means that the electrons are being removed from an increasingly cationic species. the smaller the halogen atom, the higher the ionization energy.
What is the general trend of the electron affinity in the periodic table?
this exothermic process expels energy in the form of heat and in an amount known as the electron affinity. By convention, electron affinity is reported as a positive energy value, even though by the conventions of thermodynamics, exothermic processes have negative energy changes. Regardless of the sign, remember that electron affinity is released energy. The stronger the electrostatic pull (that is, the Zeff) between the nucleus and the valence shell electrons, the greater the energy release will be when the atom gains the electron. Thus, electron affinity increases across a period from left to right. Because the valence shell is farther away from the nucleus as the principal quantum number increases, electron affinity decreases in a group from top to bottom.
What is the general trend of the electronegativity in the periodic table?
Electronegativity is a measure of the attractive force that an atom will exert on an electron in a chemical bond. The greater the electronegativity of an atom, the greater its attraction for bonding electrons. Electronegativity values are related to ionization energies: the lower the ionization energy, the lower the electronegativity; Electronegativity increases across a period from left to right and decreases in a group from top to bottom. Electronegativity can also be called “ nuclear positivity.” It is a result of the nucleus’ attraction for electrons; that is, the Zeff perceived by the electrons in a bond.
What are the general trends of the periodic table?
- Cs = largest, least electronegative, lowest ionization energy, most endothermic electron affinity
- F = smallest, most electronegative, highest ionization energy, most exothermic electron affinity
- Left → Right
- Atomic radius ↓
- Ionization energy ↑
- Electron affinity ↑
- Electronegativity ↑
- Top → Bottom
- Atomic radius ↑
- Ionization energy ↓
- Electron affinity ↓
- Electronegativity ↓
What are metals?
shiny, conduct electricity well, malleable, ductile, solids, except for mercury liquid. They generally have high melting points and densities, exceptions, lithium, which has a density that is about half that of water. Metals have the ability to be deformed without breaking; the ability of metal to be hammered into shapes is called malleability, and its ability to be pulled into wires is called ductility. At the atomic level, a metal is defined by a low Zeff, low electronegativity (high electropositivity), large atomic radius, and low ionization energy. These combined characteristics make it fairly easy for metals to give up one or more electrons. Because the valence electrons of all metals are only loosely held to their atoms, they are free to move, which makes metals good conductors of heat and electricity. Multiple oxidation states.
- MeTals lose electrons to become caTions = posiTive (+) ions
- Nonmetals gain electrons to become aNions = Negative (-) ions
What are nonmetals?
• dull, poor conductors of electricity, brittle,upper right side of table, brittle with no luster, high ionization energies, electron affinities, electronegativities, small atomic radii, poor conductors
What are metalloids?
share both charactersitics, physical properties, densities melting points and boiling points vary widely. Include boron, silicon, germanium, arsenic, antimony, tellurium, and polonium,
What are alkali metals?
lower densites that mothers, alkali metals have only one loosely bound electron in their outermost shells. Their Zeff values are very low, giving them the largest atomic radii of all the elements in their respective periods. This low Zeff value also explains the other trends: low ionization energies, low electron affinities, and low electronegativity’s. Alkali metals easily lose one electron to form univalent cations, and they react very readily with nonmetals, especially the halogens, as in NaCl.
What are alkaline earth metals?
characteristic metal properties most similar to alkali, therefore are called active metals not naturally found in elemental(neutral) state slightly higher effective nuclear charges and thus slightly smaller atomic radii
What are halogens?
highly reactive nonmetals, seven valence electrons all different states, chemical reactivity is more uniform, and due to their very high electronegativities and electron affinities, they are especially reactive toward the alkali and alkaline earth metals. In this group, fluorine has the highest electronegativity, and it has the highest electronegativity of all the elements. The halogens are so reactive that they are not naturally found in their elemental state but rather as ions (called halides)
What are the noble gases?
inert, low chemical reactivities, high ionization energies, no tendency to gain or lose electrons no electronegativities, low boiling points and gases at room temp
What are transition metals?
: low electron affinities, low ionization energies, low electronegativities, very hard high melting and boiling points, malleable and good conductors loosely held electrons filling the d subshell, different oxidation states, and losing diff. numbers of electrons. Form different complex ions forming colored solutions with nonmetals low solubility
What are chemical bonds?
strong attractive forces
What are some exceptions to the octet rule?
- • Hydrogen is excused from the octet rule because it doesn’ t have enough “ space” for eight electrons, it only has the one s-subshell, which can hold a maximum of two electrons.
- • Lithium, beryllium, and boron are just lazy— they have enough room because they have both s- and p-orbitals to hold a total of eight electrons, but they’ d rather not put in all the hard work to getting all eight.
- • All the elements in period 3 and greater have extra storage space, so they can hold more than eight electrons if necessary.
What is the significance of ionic bonding?
one or more electrons from an atom with lower ionization energy, typically a metal, transferred to an atom with greater electron affinity toward nonmetal. Positively charged cation is electrostatically attracted to the negatively charged anion. Electronegativity difference greater than 1.7. high melting and boiling points, dissolve readily, when solids from crystalline, dissociate in water and polar solvents.
What is the significance of covalent bonding?
electron pair shared between two atoms, two nonmetals, if the electron pair is shared equally, the covalent bond is nonpolar; and if the pair is shared unequally, the bond is polar. If the shared electrons are contributed by only one of the two atoms, the bond is called coordinate covalent. Covalent compounds contain discrete molecular units with relatively weak intermolecular interactions. As a result, these compounds tend to have lower melting and boiling points. In addition, since they do not break down into constituent ions, they are poor conductors of electricity in the liquid state or in aqueous solutions.
What are the characteristic bond lengths and energies?
- Bond length is the average distance between the two nuclei of the atoms involved in a bond. As the number of shared electron pairs increases, the two atoms are pulled closer together, resulting in a decrease in bond lengths.
- Bond energy is the energy required to break a bond by separating its components into their isolated, gaseous atomic states. the greater the number of pairs of electrons shared between the atomic nuclei, the more energy is required to “ break” the bond(s) holding the atoms together. Thus, triple bonds have the greatest bond energy, and single bonds have the lowest bond energy. the greater the bond energy is, the “ stronger” the bond.
What is the significancee of polarities? what is a polar molecule?
the atom with the higher electronegativity gets the larger “ share” of the electron pair(s). A polar bond is a dipole, with the positive end of the dipole at the less electronegative atom and the negative end at the more electronegative atom. Nonpolar covalent bond- atoms that have identical or nearly identical electronegativities share electron pair(s), they do so with equal distribution of the electron, no separation of charge across the bond, only same elements have purely equal distribution. H2,N2,O2,F2,Cl2,Br2,I2 Polar covalent bonds- .4-1.7 separation of charge across bond. results in the more electronegative element acquiring a greater portion of the electron pair(s) and taking on a partial negative charge, δ − , and the less electronegative element acquiring a smaller portion of the electron pair(s) and taking on a partial positive charge, δ +.
dipole movement. μ =vector quantity. q=charge magnitude r=distance between two partial charges In a coordinate covalent bond, the shared electron pair comes from the lone pair of one of the atoms in the molecule, while the other atom involved in the bond contributes nothing. The same bond connectivity and differ only in the arrangement of the electron pairs, then these structures represent different resonance forms for a single compound.
What are valence electrons and describe their structures.
- V is the normal number of electrons in the atom’ s valence shell, Nnonbonding is the number of nonbonding electrons, and Nbonding is the number of bonding electrons. The charge of an ion or compound is equal to the sum of the formal charges of the individual atoms comprising the ion or compound.
- Valence shell electron pair repulsion theory (VSEPR theory)- three-dimensional arrangement of atoms surrounding a central atom is determined by the repulsions between the bonding and the nonbonding electron pairs in the valence shell of the central atom. These electron pairs arrange themselves as far apart as possible, thereby minimizing the repulsive forces
- Electronic geometry describes the spatial arrangement of all pairs of electrons around the central atom, including the bonding and the lone pairs. In contrast, the molecular geometry describes the spatial arrangement of only the bonding pairs of electrons.
What are London dispersion forces?
• London Dispersion forces: In a given instantaneous moment, the electron density may be unequally distributed between the two atoms. This results in a rapid polarization and counterpolarization of the electron cloud and the formation of short-lived dipole moments. these dipoles interact with the electron clouds of neighboring compounds, inducing the formation of more dipoles. The attractive interactions of these short-lived and rapidly shifting dipoles are known as dispersion forces, or London forces. Large molecules with electrons that are far from the nucleus are easily polarizable and thus possess greater dispersion forces.
What are dipole-dipole interactions?
• Dipole-Dipole Interactions: polar molecules form The positive region of one molecule is close to the negative region of another molecule. Dipole— dipole interactions are present in the solid and liquid phases but become negligible in the gas phase because of the significantly increased distance between gas particles. Polar species also tend to have higher melting and boiling points than those of nonpolar species of comparable molecular weight.
What are hydrogen bonds and what are their strength?
• A hydrogen bond is a specific, unusually strong form of dipole– dipole interaction, which may be intra- or intermolecular. Not bonds, no sharing of electrons. When hydrogen is bound to one of three highly electronegative atoms— fluorine, oxygen, or nitrogen— the hydrogen atom carries only a small amount of the electron density in the covalent bond.
What are sigma bonds?
• Sigma bonds allow for free rotation about their axes because the electron density of the bonding orbital is a single linear accumulation between the atomic nuclei. When the orbitals overlap in such a way that there are two parallel electron cloud densities, a pi (π ) bond is formed. Pi bonds do not allow for free rotation because the electron densities of the orbital are parallel.
Describe the properties of the gaseous state.
- The atoms or molecules in a gaseous sample move rapidly and are far apart from each other. In addition, only very weak intermolecular forces exist between gas particles; this results in certain characteristic physical properties, such as the ability to expand to fill any volume and to take on the shape of a container
- standard temperature and pressure, or STP, which refers to conditions of 273.13 K (0° C) and 1 atm. standard state conditions- STP (273 K and 1 atm) is generally used for gas law calculations; standard state conditions (298 K and 1 atm)
What are ideal gases and what are their requirements?
- ideal gases: An ideal gas represents a hypothetical gas whose molecules have no intermolecular forces and occupy no volume. Although real gases deviate from this ideal behavior at high pressures and low temperatures
- kinetic molecular theory:
- Gases are made up of particles whose volumes are negligible compared to the container volume.
- Gas atoms or molecules exhibit no intermolecular attractions or repulsions.
- Gas particles are in continuous, random motion, undergoing collisions with other particles and the container walls.
- Collisions between any two gas particles are elastic, meaning that there is conservation of both momentum and kinetic energy.
Describe the average kinetic energy and the effect of temperature.
- The average kinetic energy of gas particles is proportional to the absolute temperature (in Kelvin) of the gas, and it is the same for all gases at a given temperature, irrespective of chemical identity or atomic mass.
- k=Boltzmann constant.
- Urms=resultant quantity
- R is the ideal gas constant
- M is the molecular mass
- bell-shaped curve flattens and shifts to the right as the temperature increases, indicating that at higher temperatures, more molecules are moving at higher speeds.
- The higher the temperature, the faster the molecules move. The larger the molecules, they slower they move.
What is diffusion and effusion?
- r=diffusion M=Molar masses
- This equation is used to determine relative rates of diffusion or effusion.
- Diffusion: When gases mix with one another. The kinetic molecular theory of gases predicts that heavier gases diffuse more slowly than lighter ones because of their differing average speeds. All gas particles have the same average kinetic energy at the same temperature, it must be true that particles with greater mass travel at a slower average velocity.
- Effusion: When a gas moves through a small hole under pressure. the flow of gas particles under pressure from one compartment to another through a small opening
What is avogadro’s principle?
•that all gases at a constant temperature and pressure occupy volumes that are directly proportional to the number of moles of gas present. Equal amounts of all gases at the same temperature and pressure will occupy equal volumes. One mole of any gas, irrespective of its chemical identity, will occupy 22.4 liters at STP
- where n1 and n2 are the number of moles of gas 1 and gas 2, and V1 and V2 are the volumes of the gases
- PV = nRT pressure (P), volume (V), temperature (T), and number of moles (n), R=8.21 × 10-2 (L· atm)/(mol· K) or 8.314 J/(K· mol)
- We define density as the ratio of the mass per unit volume of a substance and, for gases, express it in units of grams per liter (g/L) V2 is then used to find the density of the gas under nonstandard conditions:
What is Boyle’s Law?
• Boyle’s law is a derivation of the ideal gas law and states that pressure and volume are inversely related: When one increases, the other decreases. for a given gaseous sample held at constant temperature conditions) the volume of the gas is inversely proportional to its pressure:
What is Charles Law?
- Charles’ law is also a derivation of the ideal gas law and states that volume and temperature are directly proportional: When one increases, the other does too. The law states that at constant pressure, the volume of a gas is proportional to its absolute temperature,
- if one extrapolates the V versus T plot for a gas back to where V = 0 (as it should for an ideal gas), we find that T→ 0 K!
What are non-ideal conditions?
•when the gas atoms or molecules are forced into close proximity under high pressure and at low temperature. Under these “ nonideal” conditions, the molecular volume and intermolecular forces become significant. As the pressure of a gas increases, the particles are pushed closer and closer together. As the condensation pressure for a given temperature is approached, intermolecular attraction forces become more and more significant, until the gas condenses into the liquid state. At extremely high pressure, however, the size of the particles becomes relatively large compared to the distance between them, and this causes the gas to take up a larger volume than would be predicted by the ideal gas law. As the temperature of a gas is decreased, the average velocity of the gas molecules decreases, and the attractive intermolecular forces become increasingly significant. As the condensation temperature is approached for a given pressure, intermolecular attractions eventually cause the gas to condense to a liquid state. As the temperature of a gas is reduced toward its condensation point (which is the same as its boiling point), intermolecular attraction causes the gas to have a smaller volume than that which would be predicted by the ideal gas law. The closer the temperature of a gas is to its boiling point, the less ideal is its behavior. where a and b are physical constants experimentally determined for each gas. The a term corrects for the attractive forces between molecules (a for attractive) and as such will be smaller for gases that are small and less polarizable He, larger for gases that are larger and more polarizable Xe, and largest for polar molecules. The b term corrects for the volume of the molecules themselves. Larger values of b are thus found for larger molecules. Numerical values for a are generally much larger than those for b.
What is a compound?
- (pure substances composed of two or more elements in a fixed proportion
What is a molecule?
combination of two or more atoms held together by covalent bonds. Smallest unit of a compound that displays the identifying properties of that compound. Can be composed of two or more atoms of the same element (N2 and O2) may be composed of two or more atoms of different elements CO2 or SOCl2.
What are ionic compounds?
do not form true molecules with opposite charges arranged in the solid state, form from combinations of elements with large electronegativity differences (that sit far apart on the periodic table), such as sodium and chlorine. Molecular compounds form from the combination of elements of similar electronegativity (that sit close to each other on the periodic table), such as carbon with oxygen
What are molecular weights?
measurement of mass, sum of atomic weights of all the atoms in a molecule, units are atomic mass units (amu), formal weight of ionic compound by added up atomic weights of constituent ions by empirical formula in grams
What is a mole?
quantity of any thing (molecules, atoms, dollar bills, chairs, etc.) equal to the number of particles found in 12 grams of carbon-12.
What is avogadro’s number?
One mole of a compound has a mass in grams equal to the molecular weight of the compound expressed in amu and contains 6.022 × 1023 molecules of that compound.
What are equivalent weights?
• acid-base reactions, redox reactions, and precipitation reactions. one mole of HCl has the ability to donate one mole of hydrogen ions (H+) in solution, but one mole of H2SO4 has the ability to donate two moles of hydrogen ions, and one mole of H3PO4 has the ability to donate three moles of hydrogen ions. One mole of sodium has the ability to donate one mole of electrons, while one mole of magnesium has the ability to donate two moles of electrons. To find one mole of hydrogen ions for a particular acid-base reaction, we could “ source” those protons from one mole of HCl, or we could instead use a half-mole of H2SO4. If we’re using H3PO4, we’d only need one-third of a mole. This is what we mean by “ different capacities to act in certain ways.” How many things we are interested in. One mole of hydrogen ions (one equivalent) will be donated by one mole of HCl, but two moles of hydrogen ions (two equivalents) will be donated by one mole of H2SO4, and three moles of hydrogen ions (three equivalents) will be donated by one mole of H3PO4. Simply put, an equivalent is a mole of charge. one mole of HCl will donate one mole (one equivalent) of hydrogen ions, a certain mass amount of HCl will donate one equivalent of hydrogen ions. This amount of compound, measured in grams, that produces one equivalent of the monovalent particle of interest (protons, hydroxide ions, electrons, or ions) is called the gram equivalent weight. With the gram equivalent weight= molar mass/n (number of protons, hydroxide ions, electrons or monovalent ions. “ produced” or “ consumed” per molecule of the compound in the reaction. For example, you would need 49 grams of H2SO4 (molar mass = 98 g/mol) to produce one equivalent of hydrogen ions, because each molecule of H2SO4 can donate two hydrogen ions (n = 2). Simply put, an equivalent weight of a compound is the mass that provides one mole of charge. If the amount of a compound in a reaction is known and you need to determine how many equivalents are present, equivalents=mass of compound/gram equivalent weight.
What is normality?
measure of concentration, units are equivalents/liters. 1 N solution of acid contains a concentration of hydrogen ions equal to 1 mole/liter; a 2 N solution of acid contains a concentration of hydrogen ions equal to 2 moles/liter. The actual concentration of the acidic compound may be the same or different from the normality, because different compounds have different capacities to donate hydrogen ions. In a 1 N acid solution consisting of dissolved HCl, the molarity of HCl is 1 M because HCl is a monoprotic acid, but if the dissolved acid is H2SO4, then the molarity of H2SO4 in a 1 N acid solution is 0.5 M, because H2SO4 is a diprotic acid. Molarity=normality/n. where n is the number of protons, hydroxide ions, electrons, or monovalent ions “ produced” or “ consumed” per molecule of the compound in the reaction. There is a real benefit to working with equivalents and normality because it allows a direct comparison of quantities of the “ thing” you are most interested in. So it is very convenient to be able to say that one equivalent of acid (hydrogen ion) will neutralize one equivalent of base (hydroxide ion). The same could not necessarily be said to be true if we were dealing with moles of acidic compound and moles of basic compound. For example, one mole of HCl will not completely neutralize one mole of Ca(OH)2, because one mole of HCl will donate one equivalent of acid but Ca(OH)2 will donate two equivalents of base.
What is the law of constant competition?
states that any pure sample of a given compound will contain the same elements in an identical mass ratio.
What is the empirical and molecular formula?
The empirical formula gives the simplest whole number ratio of the elements in the compound. The molecular formula gives the exact number of atoms of each element in the compound and is usually a multiple of the empirical formula. For example, the empirical formula for benzene is CH, while the molecular formula is C6H6
What is the percent composition?
• percent composition by mass of an element is the weight percent of a given element in a specific compound. You can calculate the percent composition of an element by using either the empirical or the molecular formula; just be sure to use to the appropriate mass measurement: formula weight for empirical formula or molar mass for molecular formula. Formula weight is simply the mass of the atoms in the empirical formula of a compound. The molecular formula is either the same as the empirical formula or a multiple of it. To calculate the molecular formula, you need to know the mole ratio (this will give you the empirical formula) and the molecular weight (molecular weight ÷ empirical formula weight will give you the multiplier for the empirical formula to molecular formula conversion).
What are chemical reactions?
Combination reactions- having two or more reactants forming one product and generally have more reactants than products. A + B → C.
What are decomposition reaction?
generally have more products than reactants. C → A + B and is the opposite of a combination reaction: A single compound reactant breaks down into two or more products, usually as a result of heating or electrolysis.
What are single-replacement reactions?
an atom (or ion) of one compound is replaced by an atom of another element. Redox reactions.
What are double-displacement reactions?
elements from two different compounds swap places with each other to form two new compounds. This type of reaction occurs when one of the products is removed from the solution as a precipitate or gas or when two of the original species combine to form a weak electrolyte that remains undissociated in solution
What are neutralization reactions?
are a specific type of double-displacement reaction in which an acid reacts with a base to produce a salt.
What are net ionic equations?
usually written such as displacements, the ionic constituents of the compounds are in solution, so we can write the chemical reaction in ionic form. t’s not taking part in the overall reaction but simply remains in the solution unchanged. We call such species spectator ions. With net ionic being equations list only the elements important for demonstrating the actual reaction that occurs during a displacement reaction.
What are balancing equations?
look at Charge on each side, Number of atoms of each element. mass of the reactants consumed must equal the mass of products generated. number of atoms on the reactant side equals the number of atoms on the product side. Stoichiometric coefficients, which are placed in front of each compound, are used to indicate the number of moles of a given species involved in the reaction. When balancing equations, focus on the least represented elements first and work your way to the most represented element of the reaction (usually oxygen or hydrogen).
What are stoichiometric applications?
- most useful bit of information to glean from a balanced reaction is the mole ratio of reactants consumed to products generated. Furthermore, you can generate the mole ratio of one reactant to another or one product to another. All these ratios can be generated by a comparison of the stoichiometric coefficients.\
What is the limiting reactant?
• reactant is known as the limiting reactant (or reagent) because it limits the amount of product that can be formed in the reaction. The reactant that remains after all the limiting reactant is used up is called the excess reactant (or reagent). 1. All comparisons of reactants must be done in units of moles. Gram-to-gram comparisons will be useless and maybe even misleading. 2. It is not the absolute mole quantities of the reactants that determine which reactant is the limiting reactant. Rather, the rate at which the reactants are consumed (the stoichiometric ratios of the reactants) combined with the absolute mole quantities determines which reactant is the limiting reactant.
What are the yields?
• of a reaction is either the amount of product predicted (theoretical yield) or obtained (raw or actual yield) when the reaction is carried out. Theoretical yield is the maximum amount of product that can be generated as predicted from the balanced equation, assuming that all of the limiting reactant is consumed, no side reactions have occurred, and the entire product has been collected. Actual yield is the amount of product that you are actually able to obtain. The ratio of the actual yield to the theoretical yield, multiplied by 100 percent, gives you the percent yield,
What are the chemical kinetics?
Reactions can be spontaneous or nonspontaneous; the change in Gibbs free energy determines whether or not a reaction will occur, by itself, without outside assistance. even if a reaction is spontaneous, this does not necessarily mean that it will run quickly. In fact, nearly every reaction that our very lives depend upon, while perhaps spontaneous, proceeds so slowly that without the aid of enzymes and other catalysts,
What are the reaction mechanisms?
Many reactions proceed by more than one step, the series of which is known as the mechanism of a reaction and the sum of which gives the overall reaction. Mechanisms are proposed pathways for a reaction that must coincide with rate data information from experimental observation. The molecule A2B, which does not appear in the overall reaction, is called an intermediate. Reaction intermediates are often difficult to detect because they may be consumed almost immediately after they are formed, but a proposed mechanism that includes intermediates can be supported through kinetic experiments. One of the most important points for you to remember is that the slowest step in any proposed mechanism is called the rate-determining step, because it acts like a kinetic “ bottleneck,” preventing the overall reaction from proceeding any faster than the slowest step.
What are the reaction rates?
•Reaction Rates- take measurements of the concentrations of reactants and products and their change over time. Definition of rate- 2A + B → C. one mole of C is produced from every two moles of A and one mole of B, we can describe the rate of this reaction in terms of either the disappearance of reactants over time or the appearance of products over time. Because the reactants, are being consumed in the process of formation of the products, we place a minus sign in front of the rate expression in terms of reactants. For the above reaction, the rate of the reaction with respect to A is − Δ [A]/Δ t, with respect to B is − Δ [B]/Δ t, and with respect to C is Δ [C]/Δ t. with the stoichiometric coefficient for the reactions unequal, with the rates of change of concentrations unequal. two moles of A are consumed for every mole of B consumed, rate− Δ [A] = 2 rate− Δ [B]. for every two moles of A consumed, only one mole of C is produced; thus, we can say that the rate− Δ [A] = 2 rateΔ [C]. rate of consumption of B is equal to the rate of production of C. standard rate of reaction in which the rates with respect to all reaction species are equal, the rate of concentration change of each species should be divided by the species’ stoichiometric coefficient: aA + bB → cC + dD: Rate is expressed in the units of moles per liter per second (mol/L· s) or molarity per second (M/s).
How is the rate law determined?
- nearly all forward, irreversible reactions, the rate is proportional to the product of the concentrations of the reactants, each raised to some power with the rate is proportional to [A]x[B]y. called the rate law. k is the reaction rate coefficient or rate constant. Rate is always measured in units of concentration over time; that is, molarity/second. The exponents x and y (or x, y, and z, if there are three reactants, etc.) are called the orders of the reaction: x is the order with respect to reactant A, and y is order with respect to reactant B. The overall order of the reaction is the sum of x + y (+ z). These exponents may be integers, fractions, or zero and must be determined experimentally.
- The units of k vary depending on the order of the reaction .This formula is used for the experimental determination of the rate law or to calculate a rate given reaction data. The values of x and y usually aren’t the same as the stoichiometric coefficients. The orders of a reaction must be determined experimentally. There are only two cases in which you can take stoichiometric coefficients as the orders of reaction. The first is when the reaction mechanism is a single step and the balanced “ overall” reaction is reflective of the entire chemical process. The second is when the complete reaction mechanism is given and the rate-determining step is indicated. The stoichiometric coefficients on the reactant side of the rate-determining step are the orders of the reaction. The second trap to be wary of is mistaking the equilibrium aspect of the law of mass action for the kinetic aspect. The expression for equilibrium includes the concentrations of all the species in the reaction, both reactants and products. The expression for chemical kinetics, the rate law expression, includes only the reactants. Keq tells you where the reaction’s equilibrium position lies. The rate tells you how quickly the reaction will get there. rate constant, k. Technically speaking, it’s not a constant, because its particular value for any specific chemical reaction will depend on the activation energy for that reaction and the temperature at which the reaction takes place. for a specific reaction, at a specific temperature, the rate coefficient is constant. For a reversible reaction, the Keq is equal to the ratio of the rate constant, k, for the forward reaction, divided by the rate constant, k− 1, for the reverse reaction. notion and principles of equilibrium apply to the system only at the end of the reaction; that is, after the system has reached equilibrium. The reaction rate, while it theoretically can be measured at any time, is usually measured at or near the beginning of the reaction to minimize the effects of the reverse reaction.
How is the rate law determined experimentally?
•Values of k, x, and y in the rate law equation (rate = k[A]x>[B]y) must be determined experimentally for a given reaction at a given temperature. 1st step) write out generic rate law look for necessary data. 2) identify a pair of trials in which the concentration of one of the reactants is changed while the concentration of all other reactants remains constant. Under these conditions, any change in rate of product formation (if there is any) from one trial to the other is solely due to the change in concentration of one reactant. Let’s imagine that compound A’s concentration is constant, while the concentration of B doubled. If the rate of the formation of product C has subsequently quadrupled, then you can say to yourself, “ Doubling the concentration of B has resulted in a quadrupling of the production rate of C, so to determine the order of the reaction, y, with respect to reactant B, I need to calculate the power by which the number 2 must be raised to equal 4. Because 2>y = 4, y = 2.” And repeat for other reactant using different data from a different pair of trials, always making sure that the concentration of only the reactant whose order you are trying to determine is changed from one trial to the other while the concentration of any other reactant remains the same. replacing the x and the y (and sometimes z) with actual numbers. To determine the value of the rate constant k, you will need to plug in actual values for the reactant concentrations and the product formation rate, once you know the values for the exponent for each reactant. You can use the data from any one of the trials; pick whichever trial has the most arithmetically convenient numbers.
What is the reaction order? and what are the different order reactions?
- chemical reactions on the basis of kinetics into classes of reactions called zero-order, first-order, second-order, mixed-order, or higher-order reactions.
- Zero-order reactions- rate of formation of product C is independent of changes in concentrations of any of the reactants, A and B. These reactions have a constant reaction rate equal to the rate coefficient (rate constant) k. The rate law for a zero-order reaction is where k has units of M s− 1 dependent upon temperature; thus, it is possible to change the rate for a zero-order reaction by changing the temperature. The only other way to change the rate of a zero-order reaction is by the addition of a catalyst, which lowers the energy of activation, thereby increasing the value of k.
- First-Order Reactions- A first-order reaction (order = 1) has a rate that is directly proportional to only one reactant, such that doubling the concentration of, say, reactant A results in a doubling of the rate of formation of product C. where k has units of s− 1. A classic example of a first-order reaction is the process of radioactive decay. From the rate law, in which the rate of decrease of the amount of a radioactive isotope A is proportional to the amount of A, with the concentration of radioactive substance A at any time t can expressed in the third equation. where [Ao] is the initial concentration of A, [At] is the concentration of A at time t, k is the rate constant, and t is time. It is important to recognize that a first-order rate law with a single reactant suggests that the reaction begins when the molecule undergoes a chemical change all by itself, without a chemical interaction, and, usually, without a physical interaction with any other molecule.
- Second-Order Reactions- A second-order reaction (order = 2) has a rate that is proportional either to the product of the concentrations of two reactants or to the square of the concentration of a single reactant (and zero-order with respect to any other reactant). where k has units of M− 1s− 1. It is important to recognize that a second-order rate law often suggests a physical collision between two reactant molecules, especially if the rate law is first-order with respect to each of the two reactants.
- Higher-Order Reactions- very few— almost zero— reactions in which a single-reaction step involves a termolecular process; in other words, there are almost no elementary processes whose rate is third-order with respect to a single reactant. This is because it is almost impossible to get three particles to collide simultaneously.
- Mixed-Order Reactions- Mixed-order reactions sometimes refer to noninteger orders (fractions) and in other cases to reactions whose order varies over the course of the reaction. Fractions are more specifically described as broken-order, and in recent times, the term mixed-order has come to refer solely to reactions whose order changes over time where A is the single reactant and E is the catalyst. The result of the large value for [A] at the beginning of the reaction is that k3[A]»_space; k2, and the reaction will appear to be first-order; at the end of the reaction, k2»_space; k3[A] because [A] will have a low value, making the reaction appear to be second-order.
What are the theories of the molecular basis of the chemical reactions?
•Collision Theory of Chemical Kinetics- states that the rate of a reaction is proportional to the number of collisions per second between the reacting molecules. ot all collisions result in a chemical reaction. An effective collision (one that leads to the formation of products) occurs only if the molecules collide with each other in the correct orientation and with sufficient energy to break the existing bonds and form new ones. The minimum energy of collision necessary for a reaction to take place is called the activation energy, Ea, or the energy barrier. Only a fraction of colliding particles have enough kinetic energy to exceed the activation energy. This means that only a fraction of all collisions are effective. where Z is the total number of collisions occurring per second and f is the fraction of collisions that are effective.
What is the transition state theory
and what are the factors affecting?
When molecules collide with sufficient energy at least equal to the activation energy, they form a transition state in which the old bonds are weakened and the new bonds begin to form. The transition state then dissociates into products, and the new bonds are fully formed. For the reaction A2 + B2→ 2AB, the change along the reaction coordinate, which is a measure of the extent to which the reaction has progressed from reactants to products. transition state, also called the activated complex, has greater energy than either the reactants or the products and is denoted by the symbol ‡ . An amount of energy at least equal to the activation energy is required to bring the reactants to this energy level. Once an activated complex is formed, it can either dissociate into the products or revert to reactants without any additional energy input. Transition states are distinguished from reaction intermediates in that, existing as they do at energy maxima, transition states exist on a continuum rather than having distinct identities and finite lifetimes. A potential energy diagram illustrates the relationship between the activation energy, the heats of reaction, and the potential energy of the system. The most important features to recognize in such diagrams are the relative energies of all of the products and reactants. The enthalpy change of the reaction (Δ H) is the difference between the potential energy of the products and the potential energy of the reactants. A negative enthalpy change indicates an exothermic reaction (heat is given off), and a positive enthalpy indicates an endothermic reaction (heat is absorbed). The activated complex, the transition state, exists at the top of the energy barrier. The difference in potential energies between the activated complex and the reactants is the activation energy of the forward reaction; the difference in potential energies between the activated complex and the products is the activation energy of the reverse reaction. – Δ H = exothermic = heat given off. +Δ H = endothermic = heat absorbed.
•Factors affecting reaction rates with. Kinetics and thermodynamics should be considered separately. Note that the potential energy of the product can be raised or lowered, thereby changing the value of Δ H without affecting the value of forward Ea.
What is the reactant concentrations?
the greater the concentrations of the reactants, the greater the number of effective collisions per unit time. the reaction rate will increase for all but zero-order reactions. For reactions occurring in the gaseous state, the partial pressures of the gas reactants serve as a measure of concentration
What is the temperature affecting the reaction rate?
For nearly all reactions, the reaction rate will increase as the temperature increases. Because the temperature of a substance is a measure of the particles’ average kinetic energy, increasing the temperature increases the average kinetic energy of the molecules. Consequently, the proportion of molecules having energies greater than Ea (and thus capable of undergoing reaction) increases with higher temperature. You’ll often hear that raising the temperature of a system by 10° C will result in an approximate doubling of the reaction rate
What is the medium of the reaction rate?
rate at which a reaction takes place may also be affected by the medium in which it takes place. Some molecules are more likely to react with each other in aqueous environments, while others are more likely to react in a nonaqueous solvent, such as DMSO (dimethylsulfoxide) or ethanol. Furthermore, the physical state of the medium (liquid, solid, or gas) can also have a significant effect. Generally, polar solvents are preferred because their molecular dipole tends to polarize the bonds of the reactants, thereby lengthening and weakening them, which permits the reaction to occur faster.
What are the catalysts?
substances that increase reaction rate without themselves being consumed in the reaction. Catalysts interact with the reactants, either by adsorption or through the formation of intermediates, and stabilize them so as to reduce the energy of activation necessary for the reaction to proceed. While many catalysts, including all enzymes, chemically interact with the reactants, upon formation of the products, they return to their original chemical state. They may increase the frequency of collisions between the reactants; change the relative orientation of the reactants, making a higher percentage of the collisions effective; donate electron density to the reactants; or reduce intramolecular bonding within reactant molecules. In homogeneous catalysis, the catalyst is in the same phase (solid, liquid, gas) as the reactants. In heterogeneous catalysis, the catalyst is in a distinct phase. only effect of the catalyst is the decrease in the energies of activation, Ea, for both the forward and reverse reactions. The presence of the catalyst has no impact on the potential energies of the reactants or the products or the difference between them. This means that catalysts change only the rate of reactions, and in fact, they change the forward rate and the reverse rate by the same factor. Consequently, they have no impact whatsoever on the equilibrium position or the measure of Keq. Remember that as useful as catalysts are in biological and non-biological systems, catalysts are not miracle workers: They will not transform a nonspontaneous reaction into a spontaneous one; they only make spontaneous reactions go more quickly toward equilibrium.
What is the dynamic equilibrium of reversible chemical reactions?
•irreversible; that is, the reaction proceeds in one direction only, the reaction goes to completion, and the amount of product formed is the maximum as determined by the amount of limiting reactant present. Reversible reactions are those in which the reaction can proceed in one of two ways: forward and reverse. (From the perspective of the direction in which the overall reaction is written, the forward reaction is the one that goes from “ reactants” on the left to “ products” on the right.) Reversible reactions usually do not proceed to completion because by definition the products can react together to re-form the reactants. When the reaction system is closed and no products or reactants are removed or added, the system will eventually “ settle” into a state in which the rate of the forward reaction equals the rate of the reverse reaction and the concentrations of the products and reactants are constant. In this dynamic equilibrium state, the forward and reverse reactions are occurring— they haven’t stopped, as in a static equilibrium— but they are going at the same rate; thus, there is no net change in the concentrations of the products or reactants. At equilibrium, the concentrations of A and B are constant (though not necessarily equal), and the reactions A → B and B → A continue to occur at equal rates. Equilibrium can be thought of as a balance between the two reactions (forward and reverse). Better still, equilibrium should be understood on the basis of entropy, which is the measure of the distribution of energy throughout a system or between a system and its environment. For a reversible reaction at a given temperature, the reaction will reach equilibrium when the system’s entropy— or energy distribution— is at a maximum and the Gibbs free energy of the system is at a minimum. At equilibrium, the rate of the forward reaction equals the rate of the reverse reaction, entropy is at a maximum, and Gibbs free energy is at a minimum. This links the concepts of thermodynamics and kinetics.
What is the law of mass action?
• the law of mass action states that if the system is at equilibrium at a given temperature, then the following ratio is constant: The law of mass action is actually related to the expressions for the rates of the forward and reverse reactions.
- the law of mass action states that if the system is at equilibrium at a given temperature, then the following ratio is constant: The law of mass action is actually related to the expressions for the rates of the forward and reverse reactions.
- Because the reaction occurs in one step, the rates of the forward and reverse reactions are given by When ratef = rater, the system is in equilibrium. Because the rates are equal, we can set the rate expressions for the forward and reverse reactions equal to each other: Because kf and kr are both constants, we can define a new constant Kc, where Kc is called the equilibrium constant and the subscript c indicates that it is in terms of concentration. (When dealing with gases, the equilibrium constant is referred to as Kp, and the subscript p indicates that it is in terms of pressure.) For dilute solutions, Kc and Keq are used interchangeably. While the forward and the reverse reaction rates are equal at equilibrium, the concentrations of the reactants and products are not usually equal. This means that the forward and reverse reaction rate constants, kf and kr, are not usually equal. The ratio of kf to kr is Kc (Keq).When a reaction occurs in more than one step, the equilibrium constant for the overall reaction is found by multiplying together the equilibrium constants for each step of the reaction. When you do this, the equilibrium constant for the overall reaction is equal to the concentrations of the products divided by the concentrations of the reactants in the overall reaction, with each concentration term raised to the stoichiometric coefficient for the respective species. The forward and reverse rate constants for the nth step are designated kn and k− n, respectively.
- law of mass action defines the position of equilibrium by stating that the ratio of the product of the concentrations of the products, each raised to their respective stoichiometric coefficients, to the product of the concentrations of the reactants, each raised to their respective stoichiometric coefficients, is constant
What is the reaction quotient?
equilibrium is a state that is achieved only through time. Depending on the actual rates of the forward and reverse reactions, equilibrium might be achieved in minutes or years. At any point in time of a reaction, we can measure the concentrations of all of the reactants and products and calculate the reaction quotient. when calculating a value of Qc for a reaction, the concentrations of the reactants and products may not be constant. In fact, if Qc changes over time because the concentrations of reaction species are changing, the reaction by definition is not at the equilibrium state. Thus, the utility of Qc is not the value itself but rather the comparison that can be made between Qc at any given moment in the reaction to the known Keq for the reaction at a given temperature. Any reaction that has not yet reached the equilibrium state, as indicated by Qc < Keq , will continue spontaneously in the forward direction (consuming reactants to form products) until the equilibrium ratio of reactants and products is reached. Any reaction in the equilibrium state will continue to react in the forward and reverse direction, but the reaction rates for the forward and reverse reactions will be equal and the concentrations of the reactants and products will be constant, such that Qc = Keq. Once a reaction is at equilibrium, any further “ movement” either in the forward direction (resulting in an increase in products) or in the reverse direction (resulting in the re-formation of reactants) will be nonspontaneous.
• Qc < Keq, Δ G < 0, reaction proceeds in forward direction
• Qc = Keq, Δ G = 0, reaction is in dynamic equilibrium
• Qc > Keq, Δ G > 0, reaction proceeds in reverse direction
What are properties law of mass action?
Properties of the law of mass action-
• The concentrations of pure solids and pure liquids do not appear in the equilibrium constant expression because their concentrations do not change in the course of the reaction.
• • Keq is characteristic of a particular reaction at a given temperature: The equilibrium constant is temperature dependent.
• • Generally, the larger the value of Keq, the farther to the right we’ll find the equilibrium and the more complete the reaction.
• • If the equilibrium constant for a reaction written in one direction is Keq, the equilibrium constant for the reaction written in reverse is 1/Keq.
