An exothermic reaction is one which:
Correct answer: D. Is accompanied by evolution of heat.
- A. Takes place on heating.
- B. Is accompanied by a flame.
- C. Is accompanied by absorption of heat.
- D. Is accompanied by evolution of heat.
Explanation
In an exothermic reaction, energy is released to the surroundings in the form of heat. This is why option D is correct, as it states that the reaction is accompanied by evolution of heat. Option A is incorrect because it implies the need for heat input, which is not a defining feature of exothermic reactions. Option B is incorrect because not all exothermic reactions produce a visible flame. Option C is incorrect because it describes an endothermic reaction, where heat is absorbed rather than released.
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About Thermochemistry and Energetics of Chemical Reactions
Thermochemistry measures energy changes in chemical reactions and distinguishes exothermic from endothermic processes. Work covers systems, surroundings and state functions, internal energy, the first law of thermodynamics, enthalpy and Hess's law, including the sign conventions used when heat enters or leaves a system.
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