Rates of reaction
Rates of reaction
The catalyst is not used up in a reaction
The catalyst may react with the reactants to form an intermediate or may provide a surface for the reaction to take place
At the end of the reaction the catalyst is regenerated
A homogeneous catalyst has the SAME physical state as the reactants
A heterogeneous catalyst has a DIFFERENT physical state to the reactants
Altering rate of reaction
Concentration (Or pressure when reacting gases)
Increasing pressure increases the number of particles in the same volume. This increase the likelihood of more successful collisions. As the particles are closer together and collide more frequently.
Increasing the temperature gives the particles more kinetic energy giving more particles enough energy to overcome the activation energy increasing the rate of reaction
Use of a catalyst
A catalyst does NOT decrease the activation energy. It provides an alternate route for the reaction to take place with a lower activation energy. Doing this increases the number of particles with the necessary energy to react therefore increasing the rate of reaction
Surface area of reactants
by increasing the surface area you increase the number of particles exposed. This means there are more places for the reaction to take place increasing the rate of reaction because more collisions are successful
What is meant by rate of reaction?
Once one of the reactants has been used up completely the concentrations stop changing and the rate of reaction is 0.
rate= change in concentration/time. (The units are mol dm-3s-1
The rate of reaction is faster at the start of the reaction as each reactant is at its highest concentration
The rate of reaction slows down as the reaction proceeds, because the reactants are being used up and their concentration decrease.
Effective and ineffective collisions
A collision will only be effective if the correct 2 conditions are met.
The particles collide with the correct orientation
The particles have sufficient energy to overcome the activation energy barrier of the reaction.