3.1.4 Effect of Catalyst

Question 1

Define a catalyst.

Answer 1

• A substance that alters the rate of a reaction but itself is unchanged at the end of the reaction.

Question 2

Define a positive catalyst.

Answer 2

• Increases the rate of reaction.

Question 3

Define a negative catalyst.

Answer 3

• Decreases the rate of reaction.

Question 4

What are the characteristics of a catalyst?

Answer 4

• Changes the speed but not the yield of a reaction.
• Only a small amount is needed.
• Not used up during the reaction.

Question 5

How do catalysts speed up the rate of reaction?

Answer 5

• By providing an alternative pathway. The catalysed reaction has a lower activation energy.

Question 6

For the catalysed reaction:

Answer 6

• More colliding particles possess energy equal to or greater than the activation energy.
• Frequency of effective collisions increase, resulting in a higher rate of formation of product particles.
• Speed of reaction increases.

Question 7

Define homogeneous catalyst.

Answer 7

• Catalyst in the same phase as the reactants.

Question 8

Define heterogeneous catalyst.

Answer 8

• Catalyst in a different phase to the reactants.

Question 9

Why use a catalyst?

Answer 9

• Lowering activation energy meaning less energy required for the molecules to react.
• Less fossil fuels have to be burnt to acquire the energy to heat to these high temperatures.