Majority of reactions taking place at ordinary temperatures with ssH are
Correct answer: B. Exothermic
- A. Endothermic
- B. Exothermic
- C. Thermally unstable
- D. Reversible
Explanation
The symbol in the original stem is the enthalpy change, which did not print cleanly in the paper. Reactions that proceed readily at ordinary temperature without a continuous supply of heat are overwhelmingly those that release energy, that is exothermic ones with a negative enthalpy change. Endothermic reactions generally need heating to be maintained, which is why combustion and neutralisation happen spontaneously while thermal decomposition does not.
This question appeared on the UHS MDCAT 2025 paper, which you can sit online with every answer explained.
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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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