Simple collision theory

Define rate of reaction and give its units

Rate of reaction - change in concentration of reactant or product / time

• Measured in mol dm^-3 s^-1

Explain what happens to the rate of reaction throughout a reaction

1. Start of the reaction

   • Highest concentration of reactants

   • No products

   • Fastest rate of reaction due to most frequent collisions

2. As the reaction proceeds

   • Concentration of reactants ahs decreased

   • Concentration of products increases

   • Rate has slowed due to less frequent collisions

3. When the reaction stops

   • One of the two reactants has been used up (limiting reactant)

   • Highest concentration of products

   • Rate is 0

Explain how the collision theory affects rate of reaction (give the 2 conditions that must occur)

In order for a reaction to take place molecules must collide

• Not all collisions lead to a collision so certain conditions have to be met in order for a reaction to occur

  1. Activation energy, E_A

     • Molecules must have enough energy to overcome the E_A

  2. Orientation

     • Molecules must collide in the correct orientation

Explain how concentration affects rate

1. Higher concentration means more molecules in the same volumes

2. This leads to more frequent collisions

3. Faster rate of reaction

Explain how pressure affects rate

1. Same number of molecules in smaller volume

2. More frequent collisions

3. Faster rate of collisions

Explain how temperature affects rate

1. Increased temperature means more particles gain more kinetic energy to overcome energy barrier

2. Particles move more

3. More frequent collisions

4. More particles will now have energy greater than or equal to the activation energy

Explain how catalysts affect rate and how it does this

A catalyst speeds up the rate of chemical reaction without being used up

• A catalyst lowers the E_A by finding an alternative reaction pathway which has a lower E_A

Draw a diagram showing the concentrations of the reaction

A + 2B → C