C11 Energy Changes

Question 1

If energy is released in a reaction what type of reaction is it

Answer 1

Exothermic

Question 2

If energy is absorbed in a reaction what type of reaction is it

Answer 2

Endothermic

Question 3

Define a catalyst

Answer 3

• increases the rate of a reaction by reducing the activation energy by providing an alternative reaction pathway.
• does not alter the products of the reaction
• is not chemically changed or used up at the end of the reaction

Question 4

Name 3 examples of an Exothermic reaction

Answer 4

• Oxidation
• Combustion
• Neutralisation

Question 5

Name 2 examples of an endothermic reaction

Answer 5

• Thermal decomposition
• Reduction

Question 6

Name one everyday use of endothermic reactions

Answer 6

Sports injury pack

Question 7

Name one everyday use of exothermic reactions

Answer 7

• Self-heating cans
• Hand warmers
• Combustion in engines

Question 8

2 advantages and 2 disadvantages of hydrogen fuel cells

Answer 8

Advantages
- The only waste product is water
- Do not need to be electricitrically recharged
- Very efficient

Disadvantages
- Hydrogen is highly flammable and difficult to store
- Hydrogen often produced by non-renewable resources
- Technology not fully developed

Question 9

Describe how hydrogen fuel cells produce electricity

Answer 9

Use hydrogen and oxygen (oxygen from air) to generate a potential difference.

The overall reaction is:
2H2 (g) + O2 (g) —-> 2H2O (l)
(The hydrogen is oxidised to produce water)

Question 10

Show the two half equations of a hydrogen fuel cell

Answer 10

Half Equation 1 - 2H2 (g) + 4OH- (aq) ——> 4H2O (l) + 4e-
Half Equation 2 - O2 (g) + 2H2O (l) + 4e- —–> 4OH- (aq)