Altering factors
The rate that reactant molecules collide can be controlled by altering any of the four factors:
- temperature
- concentration
- pressure
- particle size
- use of a catalyst
Only some of the collisions that take place cause a chemical change to happen. These are called 'successful' collisions. The greater the number of 'successful' collisions, the faster the rate of a reaction.
Temperature
If the temperature is increased, the particles have more energy and so move more quickly. Increasing the temperature increases the rate of reaction because the particles collide more often.
Concentration
If the concentration of reactants is increased, there are more reactant particles moving together. There will be more collisions and so the reaction rate is increased. The higher the concentration of reactants, the faster the rate of a reaction will be.
Particle size
By decreasing the particle size of a reactant, we are increasing its surface area. A smaller particle size of reactants provides a greater surface area that collisions can take place on. The greater the surface area, the faster the rate of reaction.
Pressure
If the pressure of gaseous reactants is increased, there are more reactant particles for a given volume. There will be more collisions and so the reaction rate is increased. The higher the pressure of reactants, the faster the rate of a reaction will be.
Use of a catalyst
A catalyst can provide a surface for reactions to take place on.
Reactant molecules are held at a favourable angle for collisions to occur, increasing the likelihood of successful collisions.
