Edexcel A-Level Chemistry AS 6.3 Construct and Interpret Enthalpy Level Diagrams Showing Exothermic and Endothermic Enthalpy Changes Questions

Use marked Edexcel IAL Chemistry questions to place reactants, products and intermediates, label ΔH arrows, and distinguish reaction enthalpy from activation energy.

Exam points

Draw reactant and product levels correctly for exothermic or endothermic changes.
Label the enthalpy-change arrow with direction, value, sign, units and species.
Distinguish overall reaction enthalpy from activation energy on diagrams with intermediates.

[Maximum number: 2]

Fuels

Fuels burn in oxygen to release a lot of energy.
Many hydrocarbons and alcohols are used as fuels. During complete combustion, they produce carbon dioxide and water.

Petrol contains 2,2,4-trimethylpentane, an isomer of octane, that promotes smooth combustion.

Figure for Question Edexcel A-Level Chemistry AS 6.3 Construct and Interpret Enthalpy Level Diagrams Showing Exothermic and Endothermic Enthalpy Changes Questions question 1 — Edexcel A-Level Chemistry AS

2,2,4-trimethylpentane

Alcohols, such as methanol and ethanol, can be used as fuels either on their own or as additives in petrol.

The standard enthalpy change of combustion, $\Delta_{\mathrm{c}} H^{\ominus}$ , of 2,2,4-trimethylpentane is $-5461 \mathrm{~kJ} \mathrm{~mol}^{-1}$ .

Draw a labelled enthalpy level diagram for the complete combustion of 2,2,4-trimethylpentane.

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Edexcel A-Level Chemistry AS 6.3 Construct and Interpret Enthalpy Level Diagrams Showing Exothermic and Endothermic Enthalpy Changes Questions question 1