O-LevelChemistryRates of Reaction5070/22 · Oct/Nov 2023 · Q67 Marks

Steam reacts with carbon to produce carbon monoxide and hydrogen. steam + carbon ⇌ carbon monoxide + hydrogen The forward reaction is endothermic.

(a)Steam reacts with carbon to produce carbon monoxide and hydrogen. steam + carbon ⇌ carbon monoxide + hydrogen The forward reaction is endothermic.
(a)(i)Explain, in terms of bond making and bond breaking, why this reaction is endothermic.[2]
(a)(ii)The transfer of thermal energy in a chemical reaction is called the enthalpy change. Write the symbol for an enthalpy change. Include the sign for an endothermic enthalpy change.[1]
(b)Carbon monoxide, water and carbon dioxide are formed during the incomplete combustion of carbon-containing fuels.
(b)(i)Name one other substance formed during the incomplete combustion of carbon-containing fuels.[1]
(b)(ii)State one adverse effect of carbon monoxide.[1]
(c)Hydrogen is used in a hydrogen-oxygen fuel cell. Describe two advantages of a hydrogen-oxygen fuel cell compared with a gasoline/petrol engine. 1 2[2]

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2023). The mark or mark type is shown in brackets.

[1] bond breaking is endothermic / needs energy
[1] AND bond making is exothermic / energy given out (1)
[1] more energy is absorbed than released / less energy is released than absorbed (1)
[1] + ΔH
[1] particulates / carbon
[1] toxic / poisonous
[1] water is the only product / no carbon dioxide made (1)
[1] higher efficiency (1)
[1] quieter (1)
[1] transfer more energy per gram of fuel (1)

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