Kinetics

Rate of Reaction

There are 4 factors that affect the rate of a reaction:

1. Concentration of reactants (pressure of gases)

2. Particle size of reactants

3. Temperature

4. Presence of a catalyst

Collision Theory

A reaction will only occur if the particles collide with sufficient energy (E > E_a)

Concentration of Reactants

Increasing concentration of reactants increases rate of reaction.

1. Reaction is greatest at the start (steepest slope); greatest concentration of reactant particles

2. Reaction slows down with time as HCl is being used up (limiting factor)

3. Reaction stops when gradient = 0; All HCl has reacted.

If there are twice as many reactant particles in the same volume: this will double the collision frequency and therefore double number of successful collisions— rate doubles

Average rate of reaction = total volume of product(s) formed / time taken to form in cm³s^-1.

If the surface area of the reactants are doubled: double the number of reactant particles are exposed to the solution. This will double the collision frequency and double the number of successful collisions with energy greater than activation energy. Therefore this doubles the rate of reaction.

Effect of Temperature

Increase in temperature, means an increase in the mean kinetic energy of the particles. So they move faster, therefore their is a greater collision frequency. MANY MORE PARTICLES have energy greater than activation energy, and lead to a successful collision.

Endothermic Reactions

Energy taken in from surroundings; more chemical energy stored in products than reactants

Exothermic Reactions

Energy releases into surroundings; more chemical energy stored in reactants than products

MAXWELL-BOLTZMANN DISTRIBUTION

Catalysis

By providing an alternate pathway with a lower activation energy, without being used up, it increases the rate of reaction as more particles have energy > activation energy.

Activation Energy

Minimum amount of energy required to start a reaction.