6.1.2-3 - Factors Affecting Rates, Collision Theory, & Activation Energy

State five factors affecting the rate of a chemical reaction.

• Concentration of reactants.

• Pressure of gases (volume).

• Surface area.

• Temperature.

• Catalysts.

What is the collision theory?

Chemical reactions can only occur only when reacting particles collide with each other with sufficient energy (more than or equal to activation energy).

Describe and explain the effect of increasing temperature on the rate of reaction.

• T increases = faster reaction.

• As T increases, kinetic energy of particles increases, i.e. more energetic collisions.

• Also they move faster, so they collide more frequently.

• However, there’s no straight line relationship between rate and temperature, i.e. they’re not directly proportional to each other.

Describe and explain the effect of increasing concentration on the rate of reaction.

• Concentration increases = faster reaction.

  • More reactants = more frequent collisions.

Describe and explain the effect of increasing pressure of a gas on the rate of reaction.

• Increasing the pressure of reacting gases, is the same as increasing concentration.

• It increases the number of gas molecules in the same volume and so increases the frequency of collisions and therefore increases the rate of reaction.

• Note that volume and pressure are inversely proportional to each other. Increasing the volume retards the reaction.

Describe and explain the effect of increasing surface area.

• If solid reactants are in smaller pieces, they have a greater surface area.

• Increasing the surface area of solid reactants increases the frequency of collisions and so increases the rate of reaction.

• E.g. block of magnesium reacts slower with acid than magnesium powder.