1
Q
Stoichiometry
A
Relationship between amount of reactants and amount of products in a chemical reaction
2
Q
Law of conservation of mass
A
- The sum of masses of all reactants must be equal to sum of masses of all products
- Matter cannot be created or destroyed in a chemical reaction
- No matter is gained or lost during chemical change
3
Q
States of matter
A
- Solid
- Liquid
- Gas
- Plasma- ionised gas (mainly found in outer space)
4
Q
Determination of the state of matter
A
Matter can exist in different states depending on temperature and pressure
5
Q
Different physical properties of matter
A
Are due to:
- Different arrangement and movement of particles
- Depends on amount of kinetic energy of that particle
6
Q
Kinetic energy
A
Energy related to the motion of an object
7
Q
Properties of solids
A
- particles are closely packed
- strong forces between particles, vibrate about fixed positions
- fixed shape
- fixed volume
8
Q
Properties of liquids
A
- particles are more spread out than in solids
- weaker forces between particles, they can move past each other
- take the shape of the container
- fixed volume
9
Q
Properties of gases
A
- particles are very spread out
- negligible forces between particles, they move randomly
- no fixed shape
- no fixed volume
10
Q
Changes of state
A
Directly related to changes in temperature
- increase in temp. = increase in avg. KE of particles in a substance
- when heated, particles gain KE + able to intermolecular forces that exist between them
- results in a change of state
11
Q
Intermolecular forces
A
Attractive forces that exist between particles
12
Q
Changes of state:
- SOLID to LIQUID
- LIQUID to GAS
- SOLID to GAS (no liquid state)
- GAS to LIQUID
- LIQUID to SOLID
- GAS to SOLID (no liquid state)
A
- Melting (energy absorbed)
- Evaporation/Boiling (energy absorbed)
- Sublimation (energy absorbed)
- Condensation (energy released)
- Freezing (energy released)
- Deposition (energy released)
13
Q
Evaporation vs. Boiling
A
Evaporation:
- change of a liquid to a gas
- BUT only takes place at surface of a liquid
- can occur at temperatures below BP of liquid
Boiling:
- change of a liquid to a gas
- takes place throughout liquid (bubbles of gas are formed within the liquid, not only at surface)
- occurs at a specific temperature
14
Q
Steps of the heating curve of a solid
A
- Upward slopes, temp. increases as substance is heated
- KE of particles increases, and they vibrate faster
- BUT, during changes of state, temp. remains constant. At these points, energy is used to overcome intermolecular forces between particles
- During melting, energy input is used to overcome intermolecular forces that hold particles in solid in fixed positions
- During boiling, energy input is used to overcome intermolecular forces that hold particles in liquid together
- Hence, during changes of state, temp. remains constant
- Once change of state is complete, temp. starts to increase again
15
Q
Elements
A
- made up of same kind of atom
- can’t be broken down by chemical means into a simpler substance
- can be divided into metals, non-metals and metalloids (properties of both)
16
Q
Atom
A
- smallest particle that shows characteristic properties of that element
17
Q
Compounds
A
A substance composed of two or more different elements that are chemically combined
- when atoms of different elements react, they lose their characteristic properties
- properties of the elements are replaced by those of new compound formed in chemical reaction
18
Q
Molecule
A
Consists of two or more atoms that are chemically bonded together
19
Q
Properties of molecules
A
- not all molecules can be classes as compounds, as they are composed of same kind of atom bonded together
- electrically neutral, although some have a dipole
20
Q
Mixture
A
Composed of two or more substance that aren’t chemically combined- each substance retains its original properties
21
Q
Homogeneous mixture
A
Has uniform composition throughout eg. solutions
- different components are NOT chemically combined
- but don’t separate physically on standing
22
Q
Heterogeneous mixture
A
Has a non-uniform composition throughout eg. air
- will separate into two layers on standing
23
Q
Solution
A
Composed of a solute dissolved in a solvent
24
Q
Concentration of the solution
A
Amount of solute dissolved in a known volume of a solution
25
Examples of solutions
1. Solid/solid: alloys eg. steel (iron and carbon)
2. Solid/liquid: copper sulphate solution
3. Liquid/liquid: wine (ethanol and water)
4. Gas/liquid: hydrochloric acid (hydrogen chloride in water)
26
Fractional distillation
Where a complex mixture can be separated into fractions because the different components have different BP
- fractions with lower BP rise higher up the column, where it's cooler before they condense
27
Chemical reactions
Involve formation of new chemical substances
- differ from physical changes that only involve a change of state with no new substances being formed
- atoms present in reactants are rearranged and join together to form products
- chemical change taking place during a chemical reaction can be represented by a chemical equation
28
Law of conservation of mass
Mass is conserved in a chemical reaction
- number and type of each atom must be the same in the reactants and products
- in a chemical reaction, atoms aren't created or destroyed, they are only rearranged to form new products
29
Diatomic molecules
Two atoms bonded together
| - 7 elements that are diatomic (Hydrogen, oxygen, nitrogen) and then group 17 elements
30
Relative atomic mass (Ar)
The weighted average mass of an atom compared to 1/12 mass of an atom of Carbon-12
- allows comparison of the relative masses of different atoms
31
Atomic mass unit
Mass of 1/12 of an atom of Carbon-12
| - atom of C-12 has a mass of exactly 12 amu
32
Why is Carbon-12 used as the reference for RAM?
Its mass can be accurately measured
| - most abundant stable isotope of carbon
33
Natural sample of an element
- made up of a mixture of isotopes according to their relative abundance
34
Isotope
An atom of the same element with same number of protons, different number of neutrons
35
Mass spectrometer
- Abundance of isotopes of an element can be analysed using a mass spectrometer
36
Relative formula mass and relative molecular mass (Mr)
Weighed average mass of the compound compared to 1/12 the mass of an atom of Carbon-12
- allows comparison of relative masses of different compounds
37
RFM vs. RMM
| Relative formula mass vs. Relative molecular mass
RFM: sum of the RAM of all atoms in a formula unit of a substance
- mainly used for ionic compounds, that don't form molecules
RMM: sum of the RAM of all atoms in a formula unit of a substance
- used for molecular covalent substances
38
Mole concept
Used to count very small particles eg. atoms, molecules and ions
- mole concept is necessary because individual atoms are so small, it's impossible to count them
39
Mole
Amount of a substance (n) that contains the same no. of particles as there are atoms in exactly 12g of isotope C-12
40
Avogadro's constant
- no. of particles in a mole of a substance
| - value is 6.02 x 10^23 (no. of atoms in exactly 12g of isotope C-12)
41
Properties of moles
- a mole of any substance contains same no. of particles, although moles of different substances have different masses
42
Molar mass (M)
Mass in grams of one mole of a substance
Unit: g/mol
Molar mass of a substance is equal to its RAM (RFM/RMM)
43
What is a particle?
Particle = atoms, molecules, ions, formula units and electrons
In one mole of a substance there are 6.02 x 10^23 particles
44
Equation for moles, mass and molar mass
n (amount in mol)
m (mass in grams)
M (molar mass)
n = m/M
45
Equation for moles and no. of particles
n = no. of particles/ 6.02 x 12^23
46
Equation for the mass of one molecule
Mass of one molecule = Molar mass / 6.02 x 10^23
47
Empirical formula
Simplest whole number ratio of atoms in a compound
48
Molecular formula
Actual number of atoms in a compound
49
Calculating empirical formula
1. From percentage, find mass of each element in 100g of compound (% given = mass in g)
2. Find amount in mol of each element present
3. Divide each element by lowest value obtained
4. Empirical formula ratio- find the simplest whole-number ratio
50
Percentage composition by mass
Expresses the mass of each element in a compound as a percentage
Equation:
% composition = (mass of element in compound/ molar mass of compound) x 100
51
Experimental methods of determining empirical formula
1. Heat the substance, measure changes in mass
2. Calculate water of crystallisation of a hydrated compound
3. Burning a sample of a substance in an excess of oxygen (complete combustion) and analysing products of reaction
52
Water of crystallisation
Determined experimentally by heating a hydrated salt until the water evaporates, leaving the anhydrous salt
mass of hydrous salt - mass of anhydrous salt = mass of water evaporated
IB Chemistry HL
flashcards
Decks in class (9)
# Cards
