A-level Applied Science/Controlling Chemical Processes

The mole equation edit

Moles = Mass divided by the realitive atomic mass

Moles = Concentration x Volume, if this volume is in cm3 the answer must be divided by 1000!

You may be required to rearrange the equation in the exam, remember this!!

Equilibria edit

Reactions that have both a forward and reverse reaction

Dynamic equilibrium
A reaction that has both a forward and reverse which occurs at the same rate
Le Chatlier`s principle
When conditions on a system in equilibrium are changed, equilibrium will move to minimise the effect of the change.

When the pressure is increased equilibrium moves in the direction of the fewest molecules. If the temperature is increased, equilibrium moves in the direction of the endothermic reaction.

Rates of reaction edit

To increase the rate:

  • Increase the temperature.
    Particles have more energy, therefore move faster, collide more often, with energy which exceeds the activation energy.
  • Increase the concentration/pressure (Same marking point in exams).
    Increases the number of collisions, therefore more successful collisions.
  • Use of a Catalyst.
    Offers an alternative route with a lower activation energy.
  • Use smaller particles/larger surface area.
    Increases the chance of collisions

The collision theory edit

Chemical reactions happen when particles collide. Particles must collide with sufficient energy (the activation energy).

Activation energy
The minimum amount of energy required for particles to react.
Effect of a Catalyst
Adding a catalyst will speed up the rate of the forward and reverse action EQUALLY. Therefore no effect on the yield. However more product is made in a shorter amount of time.
Increasing Temperature
The system will try to decrease temperature in the forward direction it's exothermic. Therefore the system absorbs the heat (reverse direction) = endothermic therefore the equilibrium position moves to the left.

The Boltzmann distribution model edit

Please follow the internal link, you need to know;

  • The title of the X and Y axes (X=Number of particles/molecules (both accepted by examiners) Y= Energy)
  • The shape of the curve
  • Where the activation energy lies (EA)
  • Where the activation energy with a catalyst lies (EACAT)
  • The affect of an increase in temperature (Moves the right and down)
  • The affect of a decrease in temperature (Moves the left and up)

Orders of reaction edit

  • 1st Order - Doubling the concentration, doubles the rate
  • 2nd Order - Doubling the concentration increases the rate by a factor of 4
  • Zero Order - Doubling the concentration has no affect on the rate

The rate equation edit

Rate = K[A]a[B]b. K is the rate constant.


  • if a or b = 1 do not include e.g. Rate=K[A][B], both are 1st order
  • if a or b = 0 do not include at all e.g. Rate=K[B], A is zero order, so has not been included
  • if a or b = 2 include it! e.g. Rate=K[A]2[B], A is 2nd order, but B is 1st order, the overall order of reaction is therefore 3rd order.

To find the overall order of reaction just add up all the little numbers!