Rates of Reaction: collision theory, factors and rate formula

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Rates Of Reactions

Reactions can be fast or slow. The rate of a reaction is the speed in which a reaction happens. The rate of reaction depends on 4 things;

Temperature (Or pressure of gas & the size of the solid particles)

Concentration

Catalyst

Surface are of solids

Reactions are explained by collision theory. The rate of reaction simply depends on how often and how hard the reacting particles collide with one-another. The particles have to collide harder, with enough energy to react and therefore more collisions increase the rate of reaction.

The effects of concentration, temperature and surface area on the rate of reaction can be explained in terms of how often the reacting particles collide successfully.

Higher Temperature

Higher temperature increases more collisions between particles so they all move quicker colliding with one-another. The minimum amount of energy needed by the particles to react is known as the Activation Energy.

Higher Concentration

Rates of reaction

a) The rate of a chemical reaction can be found by

measuring the amount of a reactant used or the

amount of product formed over time:

Rate of reaction = amount of reactant used

time

Rate of reaction = amount of product formed

time

b) Chemical reactions can only occur when reacting

particles collide with each other and with sufficient

energy. The minimum amount of energy particles

must have to react is called the activation energy.

c) Increasingthetemperatureincreasesthespeedof

the reacting particles so that they collide more

frequently and more energetically. This increases

the rate of reaction.

d) Increasing the pressure of reacting gases increases

the frequency of collisions and so increases the rate

of reaction.

e) Increasingtheconcentrationofreactantsinsolutions

increases the frequency of collisions and so increases

the rate of reaction.

f) Increasing the surface area of solid reactants increases

the frequency of collisions and so increases the rate

of reaction.

Additional guidance:

Knowledge of specific reactions other than those in the

subject content for this unit is not expected, but

candidates will be expected to have studied examples

of chemical reactions and processes in developing their

skills during their study of this section.

Information may be given in examination questions so

that candidates can make evaluations.

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