Question detail

Which of the following statements is true about the combustion of hydrocarbons?

Try the question, check the answer, then read the explanation to understand the curriculum point.

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At a glance

MCQ

Type

practice

Style

Topic

Carbon compounds as fuels and feedstock

Question

A. It always produces soot.
B. It releases energy.
C. It requires no oxygen.
D. It produces only carbon monoxide.

Answer

The correct option is It releases energy..

Explanation

The correct option is It releases energy.. It releases energy. is correct because it directly supports the approved learning objective to write balanced equations for the complete combustion of hydrocarbons with a given formula. This belongs to Properties and combustion of hydrocarbons within Carbon compounds as fuels and feedstock, so the answer must use the correct organic chemistry context. The other options are incorrect when they confuse the organic family, formula type, reaction condition, product, or property being tested. Keep molecular formula, structural formula, displayed formula, and general formula distinct. Do not confuse alkanes with alkenes, saturated with unsaturated, cracking with combustion, polymers with monomers, or hydrocarbons with oxygen-containing alcohols and carboxylic acids. When formulae are used, preserve the stored notation exactly and explain the GCSE chemistry idea in words rather than using unsupported displayed-formula diagrams.

Common mistake

Mis‑balancing the combustion equation

Students often write the combustion of an alkane as CnH2n+2 + O2 → nCO2 + (n+1)H2O, forgetting that the oxygen coefficient must be calculated from the carbon and hydrogen atoms, leading to an unbalanced equation.

Balance the equation by first determining the number of CO2 molecules from the carbon atoms (n) and the number of H2O molecules from the hydrogen atoms ((2n+2)/2 = n+1). Then calculate the required O2: 2n+ (n+1) = 3n+1 moles of O2. The correct balanced equation is CnH2n+2 + (3n+1)/2 O2 → n CO2 + (n+1) H2O.

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