Chemistry Topic 1: Stoichiometric Relationships

Define Compound

a pure substance formed when two or more elements combine chemically

How do you ratios relate to elements combining to form compounds?

each element combines with each other in a fixed ratio

Define Mixture

two or more substances mixed together but not chemically bonded so retain their individual properties

Define Homogeneous Mixture

a mixture that has the same uniform composition throughout and consists of one phase, such as a solution or mixture of gases

How can homogeneous mixtures be separated?

through physical means, e.g. distillation, crystallisation and fractional distillation

Define Heterogeneous Mixture

a mixture that does not have uniform composition and consists of separate phases e.g. sand in water

How can heterogeneous mixtures be separated?

by mechanical means e.g. filtration or using a magnet

What is cooling?

a substances’ energy is removed and particles lose energy - temperature decreases

What is freezing?

liquid turns to a solid, particles lose energy, temp decreases

What is melting?

solid turns to a liquid, particles gain energy, temp increases

What is sublimation?

when a solid turns to a gas, particles gain energy, temp is increased

What is deposition?

when a gas turns to a solid, particles lose energy, temp is decreased

What is boiling/evaporating?

when a liquid turns into a gas, particles gain energy, temp increases

What is condensing?

when a gas turns into a liquid, particles lose energy, temp is decreased

What temp does melting occur? (water)

above 0 degrees celsuis

What temp does boiling occur? (water)

around 100 degrees celsius

What temp does freezing occur? (water)

sub 0 degrees

Balance SF4 + H20 → SO2 +HF

SF4 + 2H20→ SO2 + 4HF

Define Relative Atomic Mass

the average mass of the naturally occurring isotopes of an element relative to the mass of 1/12 of an atom or carbon 12

Define Mole

the amount of substance that contains 6.02 x 10 ^23 particles

Define Avogadro’s Constant

a unit with the value 6.02 x 10^23

give the equation to find number of moles

no. of moles = mass of substance/molar mass

give the equation to find the mass of 1 molecule of a substance

mass of 1 molecule = Mr/6.02 x 10^23

What is empirical formula?

the simplest whole number ratio of the elements present in a compound

What is molecular formula?

the total number of atoms of each element present in a molecule of the compound

How do you find moles when volume of gases are given?

no.of moles = volume of gas (dm^3) / 22.7 (dm^3)

How do you find moles when concs and vols of solutions are given?

no. of moles = conc x volume

Define theoretical yield

the maximum possible amount of product formed

Define experimental yield

the actual amount of product formed in the reaction

How do you calculate the percentage yield?

experimental yield/theoretical yield x100

Define limiting reactant:

the reactant that is not in excess and therefore determines the yield of product

How do you find the limiting reactant?

divide the no. of moles of each reactant by its coefficient in the chemical equation and the smallest number equals the limiting reactant

What does a 0.100M solution mean?

The concentration = 0.100mol/dm3

Why do people use ‘ideal gases’?

they are used to model the behaviour of real gases and be used in calculations

What two assumptions are made about ideal gases?

the molecules themselves have no volume and no forces exist between them - apart from when they collide

In what conditions do gases deviate most from ideal behaviour?

at high pressure and low temps - this is when a gas is most like a liquid so the particles are close together and forces between molecules and volume of molecules will be most significant

Give Avogadro’s Law (gas)

equal volumes of ideal gases measured at the same temperature and pressure contain the same number of particles (no.of moles of an ideal gas is proportional to its volume)

What is the relationship between pressure and volume?

inversely proportional - if pressure doubles, volume halves

What is the relationship between volume and temperature?

directly proportional - if temperature is doubled volume will double

What is the relationship between temperature and pressure?

directly proportional - if temperature is doubled, pressure will double.

Give the overall gas law equation

P1 x V1 / T1 = P2 x V2 / T2

Give the ideal gas equation

PV = nRT

What is the value of R (gas constant)

8\.31 JK^-1mol^-1

What unit does volume have in the ideal gas equation?

m^3

What unit does pressure have in the ideal gas equation?

Pa

What unit does temperature have in the ideal gas equation?

K

Define Standard Solution

a solution of known concentration

How do you work out concentrations in mol dm^-3?

conc = moles/volume

How do you work out concentrations in g dm^-3

conc - mass (g)/volume

how do you find concentration in ppm? (gas)

conc ppm = vol of gas / vol of air x 10^6