OCR A-Level Chemistry AS Breadth in chemistry (01), June 2023: Question 12

1 mark · Easy difficulty · Multiple Choice

Identify the correct statement about energy changes among four options related to combustion, bond enthalpy, activation energy, and condensation.

Practise this question

Question

Multiple choice question 12 asking 'Which statement about energy changes is correct?' with four options: A (Combustion of an alkane is endothermic.), B (In an exothermic reaction, more energy is needed to break bonds than is given out when bonds are made.), C (The activation energy is a negative value.), and D (The enthalpy change for the condensation of a gas to a liquid is a negative value.). An answer box is provided at the bottom left, with 1 mark indicated at the bottom right.
Question text

12 Which statement about energy changes is correct?

A Combustion of an alkane is endothermic.

B In an exothermic reaction, more energy is needed to break bonds than is given out when

bonds are made.

C The activation energy is a negative value.

D The enthalpy change for the condensation of a gas to a liquid is a negative value.

Your answer [1]

Mark scheme

Show the mark scheme Mark scheme showing question number 12, correct answer D, 1 mark, and AO1.1 assessment objective.

12 D 1 AO1.1

How to answer it

Evaluating Statements About Energy Changes

What this question tests

This question assesses your foundational understanding of thermochemistry concepts at AS Level (AO1.1). You need to recall definitions and core principles surrounding enthalpy changes, bond breaking and forming, activation energy, and state changes (condensing/boiling).

Question 12 [1 Mark]

Analyzing the Statements

✅ Correct Answer: D

Condensing a gas into a liquid is a state change where intermolecular bonds or forces are formed. Bond formation always releases energy to the surroundings, making the enthalpy change negative ( ΔH < 0 ).

💡 Key Knowledge

  • Exothermic: Energy released, ΔH is negative. More energy is given out making bonds than is taken in to break them.
  • Endothermic: Energy absorbed, ΔH is positive.
  • State changes: Going from gas -> liquid -> solid forms forces, releasing energy (exothermic).

🧠 Exam Technique

Evaluate each statement systematically by crossing out the obviously false ones first. Do not rush multiple-choice questions; read every option to ensure you pick the most scientifically accurate statement.

❌ Common Errors & Distractors

  • Statement A: Combustion reactions release heat to warm things up; they are strongly exothermic, not endothermic.
  • Statement B: In an exothermic reaction, more energy is released making bonds than is required to break them.
  • Statement C: Activation energy is the minimum energy required to start a reaction and is always a positive value.
Mark Scheme Allocation: 1 mark awarded for selecting D.

Topics

Module 3: Periodic table and energy · Module 4: Core organic chemistry · 3.2 Physical chemistry · 4.1 Basic concepts and hydrocarbons

Question and mark scheme from the OCR A-Level Chemistry examination, AS Breadth in chemistry (01), June 2023. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.