Question detail
Which of the following represents a balanced equation for the cracking of octane (C8H18) to produce ethene (C2H4)?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Alkanes
Question
- A. C8H18 → 2C2H4 + C4H10
- B. C8H18 → 4C2H4 + C2H6
- C. C8H18 + O2 → 4C2H4 + 2H2O
- D. C8H18 → 3C2H4 + C2H6 + C2H2
Answer
C8H18 → 2C2H4 + C4H10
Explanation
The correct option is C8H18 → 2C2H4 + C4H10. C8H18 → 2C2H4 + C4H10 is the best answer because it directly supports the AQA A-Level Chemistry objective to write equations for cracking reactions. This reasoning is anchored to Fractional distillation and cracking in Alkanes, and it separates cracking from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Incorrect Cracking Equation
Students often write the cracking equation without balancing the number of atoms on both sides, leading to incorrect stoichiometry.
To fix this, ensure that the number of each type of atom is the same on both sides of the equation. For example, when cracking hexane (C6H14) into ethene (C2H4) and butane (C4H10), write the balanced equation: C6H14 → C2H4 + C4H10. Check that there are 6 carbons and 14 hydrogens on both sides.
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