Stoichiometric Relationship Flashcards
Matter can exist in different states of matter depending on?
The temperature and pressure
what is dependent on the amount of kinetic energy that the particles possess?
the different arrangement and movement of the particles.
What is kinetic energy
the energy related to the motion (or movement) of an object
What are Changes of state at constant pressure directly related to ?
changes in temperature.
What causes changes in states of matter?
- When heated, the particles of a substance gain kinetic energy
- They are able to overcome the intermolecular forces that exist between them
- This results in a change of state
What is sublimation and what happens to heat for it to happen?
- Solid to gas
- Heat is absorbed
What is deposition and what happens to heat for it to happen?
-Gas to solid
- heat is released
What is evaporation and what happens to heat for it to happen?
-liquid to gas
- heat is absorbed
What is boiling and what happens to heat for it to happen?
- liquid to gas
- Heat is absorbed
What is condensation and what happens to heat for it to happen?
- Gas to liquid
- Heat is released
What is freezing and what happens to heat for it to happen?
- Liquid to solid
- heat is released
What is melting and what happens to heat for it to happen?
- Solid to liquid
- Heat is absorbed
Provide examples of substances that undergo sublimation at atmospheric pressure (3)
- Iodine
- Carbon Dioxide
- Ammonium Chloride
How does evaporation differ from boiling?
- Evaporation differs from boiling in that it takes place only at the surface of a liquid and can occur at temperatures below the boiling point of the liquid
- Boiling occurs at a specific temperature and takes place throughout the liquid. Bubbles of gas are formed within the liquid, not only at the surface.
How can changes in state be represented in equations? (3)
- Melting: H2O (s) → H2O (l)
- Sublimation: I2 (s) → I2 (g)
- Condensation: H2O (g) → H2O (l)
Why is it that during a change in state the temperature remains constant?
At these points, the energy is being used to overcome the intermolecular forces that exist between the particles.
What is the density of water in g/cm^{3}
1.00 g/cm^{3}
What is an atom?
It is the smallest particle that shows the characteristic properties of that element
What is an element?
is made up of the same kind of atom and cannot be broken down by chemical means into a simpler substance.
How many element on the periodic table occur naturally
92 Elements
What are metalloids
These are elements that have properties of both metals and non-metals
What is a compound?
it is made up of two or more different elements that are chemically combined.
Provide examples of compounds that exist as discrete molecules?
- Water (H2O)
- Ethanol ( C2H5OH)
- Carbon Dioxide (CO2)
What is a molecule?
It consists of two or more atoms that are chemically bonded together. The atoms can be the same, as in O2, or different, as in H2O.
Why are molecules such as H2, O2, N2 not compounds?
It is because they are composed of the same kind of atom bonded together.
What is a mixture?
It is composed of two or more substances that are not chemically combined, meaning that each substance retains its original properties.
What is a homogeneous mixture?
A homogeneous mixture has the same composition throughout
What is a heterogeneous mixture?
A heterogeneous mixture has a non-uniform composition.
How can homogeneous mixtures be separated?
Through fractional distillation which is base on the principle that elements have different boiling points
What is fractional distillation?
This is a is a technique that is used to separate the components of a mixture based on their different boiling points.
What is concentration?
This is the amount of solute dissolved in a known volume of a solution
Why is the resultant volume of the mixture of ethanol and water less than the individual volumes?
This is caused by the close packing of the ethanol and water molecules when they are mixed together.
What do we call liquids that cannot mix together
immiscible i.e Oil and Water
Why can heterogeneous mixtures be separated by physical means?
This is because they form layers when mixed together, they don’t form a uniform mixture
What does the law of conservation of mass state?
mass is conserved in a chemical reaction
What are stoichiometric coefficients and do they do?
- These are the numbers in front of each formula in a balanced equation
- They tell us the molar ratios of the reactants and products in a balanced equation
What types of reactions allow the use of stoichiometric coefficients as fractions?
In combustion reactions
Define a precipitate and identify it in a chemical reaction between aqueous silver nitrate, AgNO3, and aqueous sodium chloride, NaCl
- Precipitate is an insoluble solid that forms out of a solution
- AgNO3 (aq) + NaCl (aq) → AgCl (s) + NaNO3 (aq)
- AgCl (s), is the precipitate
Provide examples of elements that exist as diatomic molecules under standard conditions
hydrogen (H2)
oxygen (O2)
nitrogen (N2)
fluorine (F2)
chlorine (Cl2)
bromine ( Br2)
iodine ( I2)
what is relative atomic mass?
This is the weighted average mass of an atom compared to 1/12 the mass of an atom of carbon-12.
What is an atomic mass unit?
The mass of 1/12 of an atom of carbon-12
Why is carbon-12 used as a reference?
It is because its mass can be accurately measured and it is the most abundant stable isotope of carbon.
What is the relative formula (or molecular) mass (Mr) of a compound
This is the weighted average mass of the compound compared to 1/12 the mass of an atom of carbon-12.
What is the difference between relative formula (RFM) mass and relative molecular mass (RMM) ?
RFM is used with Ionic compounds such as NaCl and RMM is used with covalent compounds such as O2, CO2, H2O
What is amount of substance (n)?
The amount of substance is a measure of the number of specified elementary entities in a sample
What elementary particles are referred to by amount of substance?
Elementary entities can refer to atoms, molecules, ions, electrons or any other particle.
What is the Avogadro constant?
- (symbol L or NA) is a proportionality factor that relates the amount of substance with the number of particles.
- 6.02 X 10^{23} mol^{-1}
What is the difference between the Avogadro constant and the Avogadro number?
The Avogadro number is dimensionless
What is molar mass?
This is the mass in grams of one mole of a substance. The unit for molar mass is grams per mole (g mol-1)
What is the difference between molar mass and relative atomic mass?
Relative molecular mass is dimensionless with molar mass having a unit of g mol^{-1}
What is the relationship between moles, mass and molar mass?
n (mol) = (mass (g) )/ (Molar mass (g mol−1))
How is the mass of one molecule of a substance calculated?
Mass of one molecule = (molar mass of substance) / (Avogadro constant)
What is the empirical formula?
This is the lowest whole number ratio of atoms (or ions) in a compound.
What is the molecular formula?
This is the actual number of atoms in a compound.
What is percentage composition by mass?
It expresses the mass of each element in a compound as a percentage
How do you calculate the percentage by mass of an element in a compound?
Percentage composition=|(mass of element in compound) / (molar mass of compound) |×100%
What possible errors are present when doing the combustion of magnesium experiment for determining Empirical formula of magnesium-oxide? (3)
- The magnesium used was not pure
- The product was something other than magnesium oxide (such as magnesium nitride, Mg3N2)
- Some product was lost when the lid was removed to allow oxygen in
In an experiment to calculate water of crystallization, what are the assumptions made with this method?
- The mass change is only due to the water lost from the hydrated salt
- The crucible does not absorb water
- The anhydrous salt does not decompose
How to determine the molecular formula of a compound given the Empirical formula?
- Find the molar mass of the compound
- Find the molar mass of the empirical formula
- Molar mass of compound / molar mass of the empirical formula, gives a scalar
- Multiply this by the empirical formula to get molecular formula
What was stated in Dalton’s atomic theory?
- Atoms are tiny particles made of elements
- Atoms cannot be divided
- All the atoms in an element are the same
- Atoms of one element are different to those of other elements
What did Thompson discover about electrons? (3)
- They have negative charge
- They can be deflected by electromagnetic fields
- They have very small mass
Explain the current model of the atom
- Protons and neutrons are found in the nucleus
- Electrons orbit the nucleus in shells
- The nucleus is tiny compared to the total volume of atom
- Most of atom’s mass is in the nucleus
- Most of the atom is empty space between the nucleus and the electrons
What is the charge of a proton and an electron?
proton = +1
Electron = -1
Which two particles make up most of an atom’s mass?
Protons and neutrons
What does the atomic number show about an element?
Atomic number = number of protons in an atom
How to calculate the number of neutrons?
Number of neutrons = mass number - atomic number
Define the term isotope
Atoms of the same element with different number of neutrons and therefore different mass number
Why do different isotopes of the same element react in the same way? (2)
- Neutrons have no impact on the chemical reactivity
- Reactions involve electrons, isotopes have the same number of electrons in the same arrangement
define relative atomic mass
The weighted mean mass of an atom of an element compared with one twelfth of the mass of an atom of carbon -12
Define relative isotopic mass
The mass of an atom of an isotope compared with one twelfth of the mass of an atom of the carbon-12
The relative isotopic mass is same as which number ?
mass number
what two assumptions are made when calculating mass number?
- Contribution of the electron is neglected
- Mass of both proton and neutron is taken as 1.0 u
How to calculate the relative molecular mass and relative formula mass?
Both can be calculated by adding the relative atomic masses of each of the atom making up the molecule of the formula
What are the uses of mass spectrometry? (3)
- identify unknown compounds
- Find relative abundance of each isotope of an element
- Determine structural information
What does the principal quantum number indicate?
The shell occupied by the electrons
What is a shell?
A group of orbitals with the same principal quantum number
How many electrons can the 1st shell hold?
2
How many electrons can the 2nd shell hold?
8
How many electrons can the 3rd shell hold?
18
How many electrons can the 4th shell hold?
32
What is an orbital?
A region around the nucleus that can hold up to two electrons with opposite spins
How many electrons can an orbital hold?
2
What are the 4 types of orbitals?
- s orbital
- p orbital
- d orbital
- f orbital
what is the shape of an s orbital?
Spherical
What is the shape of a p-orbital?
Dumb-bell shape
How many orbitals are found in an S- subshell?
1
How many electrons can be held in an S-subshell
2
How many orbitals does a p- subshell have?
3
How many electrons can be held in a p-subshell?
6
How many orbitals are present in a D-subshell?
5
How many electrons can be held in a d-subshell?
10
How many orbitals are found in an F-subshell?
7
How many electrons can fill an F-subshell?
14
When using ‘electrons in box’ representation, what shape is used to represent the electrons?
Arrows
What letter is used to represent shell number?
n
From which shell onwards is S-orbital present?
n=1
From which shell onwards is p-orbital present?
n = 2
From which shell onwards is d-orbital present?
n=3
From which shell onwards is F-orbital present?
n= 4
What are the rules by which electrons are arranged in the shell? (5)
- Electrons are added one at a time
- Lowest available energy level is filled first
- Each energy level must be filled before the next one can fill
- Each orbital is filled singly before pairing
-4s is filled before 3d
Why does 4s orbital fill before 3d orbital?
4s orbital has a lower energy than 3d before it is filled
What is the electron configuration of krypton?
1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6
How can electron configuration be written in short?
- The noble gas before the element is used to abbreviate
- E.g. Li –> 1s2 2s1; Li–> [He] 2s1
How are the elements arranged in a periodic table?
Group number = number of electrons in the outer shell
What is a period on a periodic table?
The horizontal rows
What is a group on a periodic table?
The vertical columns
How is the group number related to the number of electrons?
They are arranged in the order of increasing atomic numbers
Does the group number indicate horizontal or vertical columns in the periodic table?
vertical column
What is meant by periodicity?
The repeating trends in the chemical and physical properties
What change happens across each period?
Elements change from metals to non-metals
Define first ionization energy
The energy required to remove a mole of electrons from a mole of gaseous atoms to form one mole of gaseous 1+ ions under standard conditions
Write an equation for the first ionization energy of magnesium
Mg (g) –> Mg+ (g) + e-
What are the factors that affect ionization energy?
- Atomic radius
- Nuclear charge
- Electron shielding or screening
Why does first ionization energy decrease between group 2 and 3?
- Decreases between 2 and 3 because in period 3 the outermost electrons are in p-orbitals
- Whereas in group 2 are in s-orbital, so the electrons are easier to be removed
Why does first ionization energy decrease between group 5 and 6?
- The decrease between 5 and 6 is due to the group 5 electrons in p-orbitals which are single electrons
- In group 6 the outermost electrons are spin paired, with some repulsion
-Therefore the eletrons are slightly easier to remove
Does first ionization increase or decrease between the end of one period and the start of next? Why?
- Decrease
- There is increase in atomic radius
- increase in electron shielding
Does first ionization increase or decrease down a group? why?
- Decrease
- Shielding increases –> weaker attraction
- Atomic radius increases –> distance between the outer electrons and nucleus increases–> weaker attraction
- increase in number of protons is outweighed by increase in distance and shielding
Describe the structure, forces and boding in every element across period 2
- Li and Be –> giant metallic; strong attraction between positive ions and delocalized electrons; metallic bonding
- B and C –> Giant covalent; strong forces between atoms; covalent
- N2, O2, F2, Ne –> Simple molecular; Weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules
Describe the structure, forces and bonding in every element across period 3
- Na, Mg, Al –> Giant metallic; strong attraction between positive ions and delocalized electrons; metallic bonding
-Si –> Giant covalent; strong forces between atoms; covalent - P4, S8, Cl2, Ar –> Simple molecular; Weak intermolecular forces between molecules; covalent bonding within molecules and intermolecular forces between molecules
