Chemistry · Oct / Nov 2019 · Paper 11 · Question 13

An energy profile diagram is shown. [diagram: energy profile with axes labelled 'energy' (vertical) and 'progress of reaction' (horizontal); a curve rises from a horizontal line labelled 'reactants' to a peak then falls to a lower horizontal line labelled 'products'; a vertical double-headed arrow labelled R spans from the reactants level down to the products level] What does the arrow R on the diagram represent?

1. Aan endothermic energy change
2. Bthe activation energy
3. Cthe energy taken in by the reactants
4. Dthe enthalpy change of the reaction

As printed in the paper