OCR A-Level Chemistry: Chapter 10 - Reaction Rates and Equilibrium

The change in concentration of a reactant or product in a given time.

Particles must have sufficient energy

Particles must collide in correct orientation

Concentration
Temperature
Use of a catalyst
Surface area of solid reactants

Reaction rate increases

Particles have more energy

Higher speed

Collide more frequently

More successful collisions

Rate increases

A 10C increase in temperature doubles the rate.

Reaction rate increases

Concentration increases

More particles per unit volume

More frequent collisions

More successful collisions

Rate increases

Monitoring the removal of a reactant.

Following the formation of a product.

Monitoring the volume of gas produced

Monitoring the loss of mass of reactants

A substance that changes the rate of a chemical reaction without undergoing any permanent change itself.

Not used up in the reaction.
May react with a reactant to form an intermediate or provide a surface for the reaction to take place.
The catalyst is regenerated at the end of the reaction.

Has the same physical state as the reactants.

Forms an intermediate

This intermediate breaks down to give the product and regenerates the catalyst

Sulphuric acid in the production of esters

Chlorine radicals in ozone depletion

Has a different physical state from the reactants.

Usually solids in contact with gaseous reactants or reactants in solution.
Reactants are adsorbed onto the surface, where the reaction takes place.
After the reaction, the products leave the surface by desorption.

Iron in making ammonia
Platinum or rhodium in reforming
Nickel in hydrogenation of alkenes
Vanadium oxide in making sulphur trioxide

Lowers activation energy
Less electricity used
Product made faster and cuts costs and increases profit
Less fossil fuels used cuts emissions of carbon dioxide

A reaction product acts as a catalyst for that reaction.

No molecules have zero energy
Area under the curve is equal to the number of molecules
No maximum energy

The peak is lower and shifted to the right

A greater proportion of molecules can overcome the activation energy

Activation energy with a catalyst is lower than normal activation energy.
Therefore a greater proportion of molecules exceed the new lower activation energy.

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and concentrations do not change.

When a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change.

Does not change the position

| Speeds up the rates of forward and reverse reactions equally

Kc = [C]^c x [D]^d / [A]^a x [B]^b

Only constant at a given temperature

| Units change depending on the reaction