Formulae, Equations and Amount of
Substance ALWAYS LOOK AT THE
SYMBOL GIVEN (g OR dm³, etc.)
Empirical Formula:
%/ram = x for each
element, x/smallest
value, then ajust
Ionic Equations: Write
out full molecular
formula, balance,
separate into ions, look
if soluble or not, then
cancel spectator ions
and re-write
Moles = mass/molar mass
OR n=m/Mr
For Gases: moles= volume(dm³)/Molar
volume(24) OR n= v/Mv (24dm³molˉ¹)
4 Solutions:
moles=concentration(moldmˉ³)Xvolume(dm³)
OR n=cv REARRAGE: c(moldm³)=n/v
WATCH OUT 4 CONVERTIONS
cm³->dm³ 1cm³->0.001dm³ 1dm³->1000g
Calculations based on reactions
To get Mass B from Mass A:
mass A -> moles A -> moles B ->
mass B
Moles A -> Moles B: moles A x ratio B/A
Calculation of No. of Particles: No.
molecules = Moles x Avogadro
=>no. MOLECULES=nx6.02x10²³
=>no. IONS=no.molecules x No. of
ions in the formula
Concentration of Solutions:
amount of solute(moles)/volume(dm³) = moldmˉ³
amount of solute (grams)/volume(dm³) = gdmˉ³
[amount of solute (grams) / amount of solution
{solute + solvent} (grams)x10^6] x 10^6/10^6=ppm
TRY N WORK IT OUT SYSTEMATICALLY! USE X IF
NEED BE!
Annotations:
video with explaining ppm in greater depth: http://www.youtube.com/watch?v=d6MxhXPmyes
Gas Volume Calculations
To get Volume B from Mass A:
mass A -> moles A -> moles of gas
B -> volume of GAS B
Moles A -> Moles B: moles A x ratio B/A
Moles of gas B -> Volume of GAS B: moles B x molar volume
Calculations for GASES
ONLY: ratio B/A x mass A =
volume of GAS B
Annotations:
For Calculations involving gases only, you can skip using the molar mass or volume because you divide and then multiply the same number. So:
ratio B/A x Mass A = volume of gas Bis all the working that is needed!
Percentage yield (%) = (actual yield/theoretical yield) x 100
Atom economy = (Mr of product
[that you want!!] x No. of
formulae of it in the equation x 100)
/ sum of Mr of all reactants
Introduction to Organic Chemistry
Atomic Structure and The Periodic Table
Energetics
Exothermic reaction = bond breaking ∴ loses
heat energy to surroundings ∴ change in
enthalpy is negative (-ΔH)
Endothermic reaction = bond making ∴ gains
heat energy from surroundings ∴ change in
enthalpy is positive (+ΔH)
The activation energy
is the energy required
by certain chemicals to
undergo a reaction
E=mcΔT
Annotations:
E=mcΔT
E- Energy transfered
m- mass
c- specific heat capacity
ΔT- change in temperature
(Specific Heat Capacity- The energy in joules (j) needed to raise the temperature of 1Kg of a substance by 1 Kelvin)
ENTHALPY OF REACTION: is when the molar quantities as written in the equation react under standard conditions (1atm pressure + a stated temp of 298K)
ENTHALPY OF FORMATION: is the enthalpy change when 1 mole of a compound is formed from its elements under standard conditions
ENTHALPY OF COMBUSTION: is the enthalpy change when 1 mol of a substance if burnt completely in oxygen under standard conditions
ENTHALPY OF NEUTRALISATION: is the enthalpy change when an acid and base react to form 1 mol of water under standard conditions
HESS'S LAW: Law which states that the energy change in an overall chemical reaction is equal to the sum of the energy changes in the individual reacti