Question detail

Which of the following best describes the standard enthalpy of formation (ΔH°f) for a compound?

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

Energetics

Question

A. The enthalpy change when one mole of the compound is formed from its elements in their standard states at 1 bar.
B. The enthalpy change when one mole of the compound reacts completely with oxygen to give CO₂ and H₂O.
C. The enthalpy change when one mole of the compound reacts with a strong base to give the corresponding salt and water.
D. The enthalpy change when one mole of the compound is dissolved in water to give a neutral solution.

Answer

The enthalpy change when one mole of the compound is formed from its elements in their standard states at 1 bar.

Explanation

The correct option is The enthalpy change when one mole of the compound is formed from its elements in their standard states at 1 bar.. The enthalpy change when one mole of the compound is formed from its elements in their standard states at 1 bar. is the best answer because it directly supports the AQA A-Level Chemistry objective to define standard enthalpy changes for formation, combustion and neutralisation where appropriate. This reasoning is anchored to Enthalpy change in Energetics, and it separates enthalpy 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

Confusing Enthalpy Changes

Students often confuse standard enthalpy changes for formation with those for combustion, leading to incorrect calculations.

To fix this, remember that the standard enthalpy change of formation refers to the enthalpy change when one mole of a compound is formed from its elements in their standard states, while the standard enthalpy change of combustion is the enthalpy change when one mole of a substance is completely burned in oxygen. Use the correct formula for each type of enthalpy change and ensure you know the definitions clearly.

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