Chemistry Midterm 1 Review Flashcards
Identify and describe the three states of matter
- Solid: mass and definitive shape
- Liquid: takes the shape of its container, but has definitive volume independent of pressure
- Gas: takes both volume and shape of its container
- Plasma: gaseous state of matter that contains appreciable numbers of electrically charged particles
Physical properties are
Characteristics that can be obtained without altering chemical composition
Chemical properties are
Characteristics that are observed as a substance reacts with another
Work has been done
Any time matter is changed, and involves the ability to do work and transfer heat
What two forms are energy found in
Kinetic energy: energy of motion
Potential energy: stored energy
What measurement calculates the amount of mass contained n a particular volume
Density (kh/m3)
Convert from Celcius to Kelvin
K= C + 273.15
The Law of conservation of matter states
There is no detectable change in the total quantity of matter present when matter converts from one type to another (chemical change), or changes state (physical change)
State the postulates of Dalton’s atomic theory
- Matter is composed of exceedingly small particles called atoms, which are the smallest unit of an element that can participate in a chemical change
- Elements consist of only one type of atom, which has a mass that is characteristic of that element and is the same for all atoms of that element. A macroscopic sample of an element will contain large numbers of atoms, all with identical chemical properties
- Atoms of one element differ in. properties from those of another element
- Compounds consist of atoms of two or more elements combined in a small, whole number ratio, that is always present in this ratio
- Atoms are neither created nor destroyed, but are instead rearranged to yield substances that are different from before the change.
Which law can be used to describe postulates 2 and 4 of Dalton’s atomic theory
Law of conservation of matter
Which two laws can be used to support postulate 3 of Daltons atomic theory
- Law of definite proportions: all samples of a given compound, regardless of source or preparation, have the same proportions of their constituent elements
- Law of multiple proportions: If elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small, whole numbers
Explain JJ Thompsons Cathode ray tube experiment
- Proved Dalton’s idea of the atom being indivisible incorrect
- Involved a cathode ray tube, in which all air was removed and 2 metals of opposite charge were placed inside
- When turned on, a visible ray appeared from the negatively charged cathode to the positively charged cathode
- Results were consistent with different metals
What were the propositions of the cathode ray tube experiment
- Cathode ray particle is an electron, which is a negatively charged subatomic particle with a mass that is 1000 times less than that of the atom
- On the whole, atoms are neutral because positive charged particles are there to balance it out
- like charges attract repel and unlike attract
- Plum pudding model: negatively charged electrons inside a bed of positive charge.
What were the conclusions of Ernest Rutherfords gold foil experiment
- The volume occupied by an atom must consist of a large amount of empty space
- A small, relatively heavy, positively charged body, the nucleus must be at the center of each atom
- Proved JJ Thompsons model to be innaccrate
Who proposed the electrically neutral neutron
Irene Joliot and James Chadwick
How were the three subatomic particles found?
- Electron- 1887- Cathode ray tube
- Proton- Gold foil experiment
- Neutron- 1932- Paraffin foil experiment
What are isotopes
Atoms of the same element that differ in mass. They have the same number of protons and electrons, but different numbers of neutrons.
The atomic number (Z) is equal to
The number of protons
The mass number (A) is equal to
Number of protons + number of neutrons
The number of neutrons is equal to
mass number (A) - atomic number (Z)
What is the defining trait of an element
Atomic number.
A Nuclide
An atom of a specific isotope
When the number of protons and neutrons is not equal the atom is
an ion (electrically charged)
How to find the atomic charge of an element
Atomic charge= number of protons - number of electrons
What is an anion
An atom that gains one or more electrons (nonmetals)
What is a cation
An atom that loses one or more electrons (metals)
What is the atomic mass equal to
Mass number. For those elements, that occur naturally as two or more isotopes, the average mass is the total of the isotopic abundance multiplied by their mass.
How can the molecular weight of a molecule be calculated?
By multiplying up the number of mol of each substance and adding their results
Define the mol
unit of measure that represents 6.022x10^23 items
What is a molecular formula
representation of a molecule that uses chemical symbols to indicate the types of atoms followed by subscripts to show the number of atoms of each type of molecule
What is the difference between H2 and 2H
H2 is a diatomic molecule, containing two atoms of hydrogen that are chemically bonded. 2H indicates two separate hydrogen atoms that are not combined as a unit
What is an empirical formula
Indicates the types of atoms present and the simplest whole-number ratio of the number of atoms (or ions), in the compund
Who formulated the periodic law and created the first periodic table
Dimitri Mendeleev: published a periodic table which ordered elements in that of increasing atomic mass. He also used the table to predict the existence of elements that would have properties that were similar but were unknown at the time
What is the periodic law
the properties of the elements are periodic functions of their atomic numbers
Describe the arrangement of the periodic table
- Arranges the elements in order of increasing order of their atomic numbers and groups atoms with similar properties in the same vertical column
- Each box represents an element and contains its atomic number, symbol, average atomic mass, and sometimes name
- Elements are arranged in seven horizontal rows, called periods or series, and 18 vertical columns, called groups
Describe characteristics of metals
Elements that are shiny, malleable, and good conductors of heat and electricity, are located on the left side of the periodic table.
Describe characteristics of nonmetals
Elements that appear dull, and are poor conductors of heat and electricity, located on the right side of the periodic table
characteristics of metalloids include
conduct heat and electricity moderately well, and possess some properties of metals and some of nonmetals, located on right side of periodic table, separating metals and nonmetals
Alkali metals
Are located in the first column of the periodic table and form compounds that consist of one atom of the element and one atom of hydrogen, all sharing similar chemical properties. (does not include hydrogen)
Alkaline earth metals
Are located in group 2 and form compounds consisting of one atom of the element and two atoms of hydrogen
Hydrogen is a unique, non-metallic element with properties similar to groups
1 and 17
Which part of the atom is not altered in chemical reactions? Which part of the atom is?
The nucleus of the atom remains the same, whilst the electrons are transferred or shared amongst molecules
What are polyatomic ions
group of bonded atoms with an overall charge
What are ionic bonds
when electrons are transferred, ionic bonds result. They are electrostatic forces of attraction (attractive forces between objects of opposite electrical charge)
What are covalent bonds
When electrons are shared, and molecules form. They are attractive forces between the positively charged nuclei of the bonded atoms and or more pairs of electrons that are located between the atoms.
How are compounds containing polyatomic and monoatomic ions formed
Consists of the name of the cation (metal), followed by the name of the anion (nonmetallic element) whose ending is replaced by the suffix-ide
Ionic compounds that contain water molecules as integral components of their crystals are called
Hydrates. They are named by first stating the anhydrous compound and then with a prefix denoting the number of hydrates. eg (sodium carbonate decahydrate)
How are compounds composed of two nonmetallic elements named
By stating the name of the more metallic element (farther to the left and/or bottom of the periodic table), followed by the name of the more nonmetallic element (farther to the right and/or top), with its ending changed to the suffix-ide. The number of atoms of each element is denoted using prefixes
How to name binary acids (comprised of hydrogen and one other nonmetallic element)
- Hydrogen is changed to the prefix “Hydro”
- The other nonmetallic name is modified by adding the suffix- ic.
- The word acid is added to the second word
How can you calculate the formula mass of a substance?
By summing up the average atomic masses of all the atoms represented in the substances formula
Why is the formula for an ionic compound referred to as the molecular mass?
The formula does not represent the composition of a discrete molecule
What is the mole of a substance?
the amount in which there are 6.022x10^23 items (avogardro’s number).
What is the molar mass of an element?
Mass in grams of 1 mole of the substance
What is precent composition and how is it calculated?
the percentage by mass of each element in a compound. It can be calculated by dividing the elements mass by the total mass and finding the percent.
Given the masses of elements in a compound, how can one determine the empirical formula
- Convert the mass number to number of moles by dividing by each elements specific molar mass
- Divide by the smallest ratio of masses, and round to the nearest whole number
- If necessary, multiply all coefficients by an integer to ensure the smallest whole number ratio is obtained
How can one determine empirical formula given percent composition?
- Convert percent to mass per 100g
- Divide by molar masses
- Divide by smallest whole number ratio
How can one convert an empirical to molecular formula?
- If actual molar mass of substance is known divide it by the mass calculated using the empirical formula
- Multiply all subscripts in the formula by the n ratio obtained
What is a solvent?
the component of the solution who’s volume is greater than all other components, and is the medium in which all other components are dissolved.
What is an aqueous solution ?
Water is the solvent
What is a solute?
The component of a solution that is present in much lower concentration than the solvent. Dilute solution is one that is lower in concentration, and concentrated solutes are high in concentration.
How is molarity defined as?
The number of moles of solute in exactly 1 liter of solution.
What is the mass percentage of a solution?
the ratio of the components mass, to the solutions mass, expressed as a percentage
What are spectator ions in a chemical reaction?
ions whose presence is required to maintain charge neutrality, but are neither chemically nor physically changed by the process, and may be eliminated from the equation.
What is a precipitation reaction?
one in which dissolved substances react to form one (or more), solid products.
When will a substance precipitate?
when solution conditions are such that its concentration exceeds its solubility. Substances that are insoluble will readily precipitate from solution.
How can one predict precipitation reactions?
- identify all the ions present in the solution and then consider if possible cation/anion pairing will result in an insoluble compound.
What is an acid-base reaction?
one in which a hydrogen ion, is transferred from one chemical species to another
How does an acid react with water?
it forms a hydromium [H30+] ion
What are strong acids?
Acids that completely react to form hydromium ions
More commonly acids belong to the group of?
Weak acids. They only partially react with water, leaving a large majority of dissolved molecules in their original form and generating a relatively small amount of hydronium ions
What is a base?
A substance that will dissolve in water and yield hydroxide ions (OH-). They do not chemically react with water, but instead dissolve and dissociate, releasing hydroxide ions directly into the solution.
What is a strong base?
One that will completely dissociate in water.
What is a weak base?
One that produces hydroxide ions when dissolved by chemically reacting with water molecules. They react only partially.
What is a neutralization reaction?
Specific type of acid-base reaction in which the reactants are an acid and a base (but not water), and the products are often a salt and water.
When is the double arrow used?
When a weak acid or base is in the equation, since it does not completely react
What is oxidation and reduction in a reaction?
Oxidation is caused by the loss of electrons
Reduction is caused by the gain of electrons
What are reducing and oxidizing agents?
A reducing agent is the species that is oxidized (loses electrons)
A oxidizing agent is one that is reduced (gains electrons)
What is an oxidation number?
The charge an atom would possess if the compound were ionic.
what is the oxidation number for an atom in elemental substance
0
What is the oxidation number for a monatomic ion?
equal to the ions charge
What are the oxidation numbers for hydrogen?
+1 when combined with nonmetals, -1 when combined with metals
What are the oxidation numbers for oxygen?
-2 in most compounds, sometimes -1 (peroxides 02^2-), very rarely -1/2 (so-called superoxides, O2^-), positive values when combined with F (values vary)
What are the oxidation numbers for halogens?
-1 for F always, -1 for other halogens except when combined with oxygen or other halogens (positive oxidation numbers in these cases, varying values)
What is the sum of all oxidation numbers for all atoms of a molecule or polyatomic ion equal to?
The charge on the molecule or ion
Define oxidation-reduction reaction?
those in which one or more elements involved undergoes a change in oxidation number. Oxidation (increase in oxidation number). Reduction (decrease in oxidation number).
A combustion reaction is a type of
Redox reaction
How are redox reactions identified?
If one or more elements undergoes a change in oxidation number
What are the 4 types of redox reactions?
- Combination: two substances form one product
- Decomposition: one reactant forms two or more products
- Displacement: elemental reactant replaces an atom in another reactant
- Combustion: reaction with oxygen to produce a flame
How to balance redox reactions?
- Write two half-reactions representing the redox process
- Balance all elements except oxygen and hydrogen
- Balance oxygen atoms by adding H2O molecules
- Balance hydrogen atoms by adding H+ ions
- Balance charge by adding electrons
- If necessary, multiply each half-reactions coefficients by the smallest possible integers to yield equal numbers of electrons in each
- Add the balanced half-reactions together and simplify by removing species that appear on both sides of the equation.
What is the limiting reactant?
The reactant present in an amount lower than required by the reaction stoichiometry, thus limiting the amount of product generated
What is the excess reactant?
reactant present in an amount greater than required by the reaction stoichiometry
What is the theoretical yield?
The amount of product that may be produced from a reaction under specified conditions, as calculated per stoichiometry
What is the actual yield?
The amount of product obtained from a reaction
How can you calculate the percent yield?
Divide the actual yield by the theoretical yield, multiply by 100
What is quantitative analysis?
the determination of the amount or concentration of a substance in a sample
What is involved in titration analysis?
- A buret is used to make incremental additions of a solution containing a known concentration of some substance (the titrant) to a sample solution containing the substance whose concentration is to be measured (analyte).
- The tirant and analyte undergo a reaction of known stoichiometry, and so measuring the volume of the titrant solution required for complete reaction with the analyte (equivalence point of titration) allows calculation of the analyte concentration.
What are signs a reaction has occurred in a titration?
- change in appearance, special dyes called indicators are added to the sample solutions to impart a change in color at or very near the equivalence point.
What is the end point in a titration?
The volume of the titrant actually measured
What is thermochemistry?
An area of science concerned with the amount of heat absorbed or released during chemical and physical changes
How can energy be defined
the capacity to supply heat or do work
what is potential energy
energy a system possesses due to the positions of the particles in a field
What is kinetic energy
energy of a system due to the motion of its particles (includes thermal energy)
What is thermal energy
kinetic energy associated with the random motion of atoms and molecules
Temperature is a
Quantitative measure of how hot or cold something is
What is heat
The transfer of thermal energy between 2 bodies at different temperatures
What is work
energy exchanged with surroundings by macroscopic motion of surroundings
What are the mechanisms by which energy is exchanged between the system and its surroundings
Heat and work
A change that releases heat is known as
Exothermic
A change that absorbs heat is known as
Endothermic
What is a calorie
unit of energy measurement. The amount of energy required to raise one gram of water by one degree C (1 kelvin)
The SI unit for heat, work and energy is
The joule
What is the heat capacity of a body of matter
the quantity of heat it absorbs or releases when it undergoes a chemical change
Heat capacity is what type of property
Extensive, and proportional to the amount of the substance
What is specific heat capacity?
the quantity of heat required to raise the temperature of 1 gram of a substance by 1 degree celcius
Specific heat capacity is what type of property
Intensive, dependent on the type of substance but not the amount
Energy entering the system is
a gain of thermal energy, and so the heat is absorbed by or work done on the system
Energy leaving a system is
A loss of thermal energy, has a negative q value. Heat is released from or work done by system
What is calorimetry?
A technique used to measure the amount of heat involved in a chemical or physical process.
What is the system?
The substance or substances undergoing a chemical or physical change
What is the surroundings ?
All other matter, including components of the measurement apparatus, that serve to either provide heat to the system or absorb heat from the system
What is a calorimeter?
device used to measure amount of heat involved in a chemical or physical process
If we initially have a high temperature substance and a low temperature substance that come into contact, what will happen?
Heat will flow from the hot temperature substance to the low temperature substance until they are both at the same temperature, known as thermal equilibrium
What is chemical thermodynamics?
the science that deals with relationships between heat, work, and other forms of energy in the context of chemical and physical processes
What is the internal energy
The total of all kinds of energy in a substance
What is the first law of thermodynamics?
the internal energy of a system changes through hear flow into or out of the system
What is expansion work (pressure-volume work)?
When a system pushes back the surroundings against a restraining pressure or when the surroundings compress the system.
What is a state function
The value of a state function depends only on the state that a system is in and not on how the state is reached. e.g internal energy
Are heat and work state functions
No
The property used to describe the thermodynamics of chemical and physical processes is known as
Enthalpy (H). It is the sum of a systems internal energy (U) and the mathematical product of of its pressure and volume
An example of a state function is
Enthalpy
A negative value for enthalpy means
Exothermic reaction
A positive enthalpy value indicates
Endothermic reaction
What is a standard state
A commonly accepted set of conditions used as a reference point for the determination of properties under other different conditions
What is the standard enthalpy of combustion
The enthalpy change when 1 mole of a substance burns (combines vigorously with oxygen)under standard state conditions. Aka “heat of combustion.”
What is the standard enthalpy of formation
The enthalpy change for a reaction in which exactly 1 mole of a pure substance is formed from free elements in their most stable states under standard state conditions.
