Fig. 2.1 shows methane (CH4) from a laboratory gas supply burning at a burner with the air hole open, so there is a plentiful supply of air. Fig. 2.1 (a) St...
Question 1 Report
Fig. 2.1 shows methane (CH4) from a laboratory gas supply burning at a burner with the air hole open, so there is a plentiful supply of air.
Fig. 2.1
(a) State what is meant by the term combustion. [1]
(b) Write a balanced symbol equation for the complete combustion of methane. [2]
(c) One product of the complete combustion of methane is a greenhouse gas. Name this gas. [1]
(d) Explain why burning methane when the air hole is closed can produce carbon monoxide instead. [2]
Answer Details
This question covers combustion, the balanced equation for burning methane, and why a limited air supply gives carbon monoxide.
(a) Meaning of combustion [1]. Combustion is a reaction with oxygen (burning) that releases heat energy [1].
(b) Balanced equation for complete combustion [2].
\[ CH_4 + 2O_2 \rightarrow CO_2 + 2H_2O \]1 mark for the correct formulae of all reactants and products, 1 mark for the equation being balanced. Check: 1 C, 4 H and 4 O on each side.
(c) Greenhouse gas produced [1]. Carbon dioxide (CO2) [1].
(d) Why a closed air hole can give carbon monoxide [2]. With the air hole closed there is a limited or insufficient supply of oxygen [1], so incomplete combustion occurs and carbon monoxide (CO) forms instead of carbon dioxide [1]. There is not enough oxygen to fully oxidise the carbon.
Exam tip: plenty of oxygen gives complete combustion (CO2 and water, clean blue flame); a poor oxygen supply gives incomplete combustion (carbon monoxide and soot, yellow smoky flame). Carbon monoxide is toxic, which is why burners are used with the air hole open.
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