Catalysts And Activation Energy (T4)

Question 1

What are catalysts?

Answer 1

Substances that speed up chemical reactions but are not used up in the process. They are still there, chemically unchanged, at the end of the reaction.

Question 2

Describe, with reference to catalysts, how bombardier beetles use hydrogen peroxide as part of their defence mechanism..

Answer 2

Bombardier beetles defend themselves by spraying a hot, unpleasant liquid at their attackers. Part of this reaction involves splitting hydrogen peroxide into water and oxygen, using the enzyme catalase as a catalyst. There are other catalysts involved here too, for example manganese (IV) oxide (AKA manganese dioxide - MnO2) - this is the chemical we use in the lab to speed up the decomposition of hydrogen peroxide. Hydrogen peroxide > water + oxygen 2H2O2(aq) > 2H2O(l) + O2(g)

Question 3

How would you measure the amount of oxygen evolved from the decomposition of hydrogen peroxide solution in a lab. State the catalyst used..

Answer 3

• put a small amount of hydrogen peroxide solution in a side-arm flask, with a weighing bottle containing manganese (IV) oxide in the middle of the solution - make sure the top of the flask is stoppered - a tube runs from the side of the flask into a beaker filled with water where it meets the bottom of a submerged measuring cylinder - shake the flask so the weighing bottle falls over and the manganese (IV) oxide mixes with the hydrogen peroxide - keep shaking to get an even mixture - measure the volume of oxygen produced at regular intervals and plot your findings on a graph

Question 4

How do you show that a substance is a catalyst?

Answer 4

The best way is to weight the substance before the reaction, and weight it again afterwards. There should be no difference in results.

Question 5

How does a catalyst work with regards to activation energy?

Answer 5

Collisions have to involve at least a small amount of energy called activation energy.

This energy can be shown on an energy diagram.

Adding a catalyst gives the reaction an alternative and easier way for it to happen, involving a lower activation energy.

If the activation energy is lower, many more collisions are likely to be successful.

Catalysts work by providing an alternative route for the reaction, involving a lower activation energy.