6 (a) What type of energy is released by hydrogen fuel cells? 6 (b) Owners of cars powered by fuel cells buy hydrogen from hydrogen filling stations - AQA - GCSE Chemistry - Question 6 - 2014 - Paper 3

1. Using hydrogen saves petrol and diesel, thus promoting the use of renewable energy sources.

2. Hydrogen usage in fuel cells does not cause pollution, contributing to environmental sustainability and reducing carbon emissions.

To calculate the energy change, we need to consider bond energies. The bonds broken are 4 H-H and 1 O-O, and the bonds formed are 4 O-H.

Energy used to break bonds:

[ \text{Energy} = 4 \times 436 \text{ kJ} + 498 \text{ kJ} = 1744 \text{ kJ} ]

Energy released in forming bonds:

[ \text{Energy} = 4 \times 464 \text{ kJ} = 1856 \text{ kJ} ]

Total energy change:

[ \text{Energy change} = \text{Energy broken} - \text{Energy formed} ]
[ \text{Energy change} = 1744 - 1856 = -112 \text{ kJ} ]

The energy level diagram should show the reactants (2H2 and O2) at a higher energy level than the products (2H2O). The activation energy should be labeled clearly as the peak of the energy curve, indicating the energy needed to initiate the reaction.