Which of the following is an endothermic process?
Correct answer: B. Photosynthesis
- A. Combustion of methane
- B. Photosynthesis
- C. Neutralisation of an acid by an alkali
- D. Condensation of steam
Explanation
Photosynthesis absorbs light energy to build glucose from carbon dioxide and water, so the products store more energy than the reactants and the enthalpy change is positive. Combustion and neutralisation both release heat, and condensation releases the latent heat that was absorbed during evaporation. A useful check is that an endothermic reaction feels cold and usually needs a continuous energy supply.
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About Exothermic and Endothermic Reactions
Exothermic reactions release heat to the surroundings and have negative enthalpy change, while endothermic reactions absorb heat and have positive enthalpy change. The topic uses energy profiles to identify reactants, products and activation energy, and includes bond energy, enthalpy diagrams, calorimetry and Hess's law for calculating overall heat changes.
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