GCSE Chemistry: Energy Changes

Every chemical reaction moves energy between the reacting substances and their surroundings, and GCSE Chemistry asks you to track that movement in three ways: through observations, through reaction profile diagrams, and — at Higher tier — through bond energy arithmetic. This quiz covers all three.

The observational layer establishes the definitions through their consequences: exothermic reactions warming their surroundings, endothermic reactions cooling them, and the everyday applications examiners cite — hand warmers running on exothermic processes, combustion of methane releasing more energy in bond formation than it consumes in bond breaking.

Reaction profiles are tested descriptively, as befits a text-based quiz: the relative energy levels of reactants and products in an endothermic reaction (products higher), what the peak of the profile represents (the activation energy barrier), and the definition of activation energy as the minimum energy colliding particles need in order to react. A negative overall energy change (−100 kJ/mol) is interpreted through a multi-select question tying the sign convention to the exothermic/endothermic distinction.

The Higher tier bond energy calculations close the set with two full worked examples: hydrogen reacting with chlorine (breaking H–H and Cl–Cl, making two H–Cl bonds, netting −184 kJ/mol) and the ammonia synthesis with its triple bond and six N–H bonds (netting −93 kJ/mol). All bond energies are given in the question, and the explanations lay out the energy-in-minus-energy-out structure explicitly — the bookkeeping discipline that keeps signs correct under exam pressure.

The distractors encode the classic inversions: swapped signs, bond making treated as endothermic, and activation energy confused with overall energy change.

• Classify reactions as exothermic or endothermic from temperature changes and applications
• Interpret reaction profile diagrams, including the position of products and the activation energy peak
• Define activation energy precisely
• Perform bond energy calculations with the energy-in minus energy-out structure (Higher)
• Interpret the sign of an overall energy change correctly

Topic scope follows the Department for Education's GCSE combined science subject content, energy changes strand: exothermic and endothermic reactions, reaction profiles, activation energy and bond energy calculations.