A reaction mixture in a beaker becomes noticeably cold. This shows that the reaction is
Correct answer: C. endothermic, since heat is absorbed from the surroundings
- A. exothermic, since heat leaves the system
- B. at equilibrium
- C. endothermic, since heat is absorbed from the surroundings
- D. catalysed
Explanation
The system draws energy from its surroundings, and since the beaker and the solution are those surroundings their temperature falls. Dissolving ammonium chloride or ammonium nitrate in water is the usual classroom demonstration, and it is the principle behind an instant cold pack. An exothermic reaction would make the beaker warm instead.
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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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