Hydrogen–oxygen fuel cells — GCSE Chemistry practice questions

Question 1

A city bus is powered by a hydrogen–oxygen fuel cell.

Four statements about the fuel cell are given.

1. Water is the only chemical product.
2. Carbon dioxide is also produced.
3. Chemical energy is changed into electrical energy.
4. The reaction in the cell is endothermic.

Which statements are correct?

Accepted Answer

A: 1 and 3. Hydrogen reacts with oxygen, so water is the only chemical product: there is no carbon to make carbon dioxide. The cell changes chemical energy into electrical energy, and the reaction releases energy, so it is exothermic.

Question 2

A city council compares a fuel-cell bus with a petrol bus.

Which statement is an advantage of the fuel-cell bus?

Accepted Answer

D: The only chemical product of the cell is water, so no carbon dioxide leaves the bus.. A fuel cell makes only water, so the bus releases no carbon dioxide, carbon monoxide or particulates at the point of use. Storage in high-pressure tanks, few refuelling stations and hydrogen made from methane are all disadvantages.

Question 3

The overall reaction in a hydrogen–oxygen fuel cell is 2H₂ + O₂ → 2H₂O.

Which row is correct?

Accepted Answer

C: hydrogen · 0 to −2 · exothermic. Hydrogen goes from 0 to +1, an increase, so hydrogen is oxidised; oxygen goes from 0 to −2, so it is reduced. The reaction releases energy, so it is exothermic.

	substance oxidised	change in oxidation number of oxygen	energy change
A	hydrogen	0 to −2	endothermic
B	oxygen	0 to −2	exothermic
C	hydrogen	0 to −2	exothermic
D	oxygen	0 to +2	exothermic