Factors Affecting Reaction Rate (College Board AP Chemistry)

• The rate of a reaction depends on the number of successful collisions between the particles
• The factors that affect the rate are:
  • Concentration
  • Pressure
  • Temperature
  • Surface area
  • The use of a catalyst

Concentration

• If the concentration increase, the amount of successful collisions increase
• Therefore, the rate of reaction increases

Effect of concentration in the rate

The diagram shows a higher concentration of particles in (b) which means that there are more particles present in the same volume than (a) so the rate of reaction increase

Pressure

• If the reactants are in gaseous state, an increase in pressure will increase the amount of successful collisions because there is less space to move
• Therefore, the rate of reaction increases

Effect of pressure in the rate

The diagram shows a higher pressure of particles in (b) which means the same number of particles occupy a smaller volume than (a) so the rate of reaction increase

Temperature

• An increase in temperature will increase the speed of the particles, so the amount of successful collisions will also increase
• Therefore, the rate of reaction increases

Effect of temperature in the rate

An increase in temperature causes an increase in the kinetic energy of the particles. The number of successful collisions increases, so the rate increases too

Surface area

• An increase in surface area will increase the amount of particles available to collide, so the amount of successful collisions will also increase
  • E.g. Going from large pieces of reactant to powder
• Therefore, the rate of reaction increases

Effect of surface area in the rate

An increase in surface area allows more particles to collide with each other. The number of successful collisions increases, so the rate increases too

The use of a catalyst

• A catalyst provides an alternate path to complete a chemical reaction
  • This new path requires less activation energy
  • The activation energy is the minimum required energy to start a reaction
• Since the energy is less, the amount of successful collisions needed must be less
• Therefore, the rate of reaction increases