Rates of reaction (O-level chemistry)
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Rates of reaction
Rate of a chemical reaction:
Is the amount of a reactant used up or product produced in a reaction per unit time
FACTORS THAT AFFECT A CHEMICAL REACTION
There are about four factors that affect a chemical change/reaction. These are:
1. A catalyst
2. Temperature
3. Concentration
4. Pressure
5. Surface area of the reactants
1. concentration
If the concentration of the reactant is increased, frequent molecular collisions will increase leading to increase in the rate reaction.
2. Temperature:
Increasing the temperature increases reaction rates because of the disproportionately large increase in the number of high energy collisions. It is only these collisions (possessing at least the activation energy for the reaction) which result in a reaction.
3. Surface area:
Increasing the surface area of a solid reactant exposes more of its particles to attack. This results in an increased chance of collisions between reactant particles, so there are more collisions in any given time and the rate of reaction increases. The surface of a solid can be increased by crushing a substance into a powder or by reducing its particle size.
4. Pressure:
This affects gaseous reactions since gases unlike solids are compressible.
Increasing pressure on gases brings reactant particles close to each other increasing the frequency of collision and hence the rate of reaction. Pressure can be increased by decreasing the volume of the container. For example, in the Haber process, a large yield of ammonia is obtained from high pressure as per the following reaction.
5.Catalyst:
increases the rate of reaction by lowering activation energy or energy barrier to the reaction.
Definition
A catalyst is substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change.
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