Which of the following is endothermic reaction?
Correct answer: B. H2 + I2 → 2HI
- A. C + O2 → CO2
- B. H2 + I2 → 2HI
- C. N2 + 3H2 ⇌ 2NH3
- D. None of the above
Explanation
The correct answer is option B: H2 + I2 → 2HI. This reaction is endothermic because it requires heat to be absorbed for the reaction to proceed, as bond-breaking in molecules like H2 and I2 demands more energy than what is released when HI is formed. Option A describes the combustion of carbon, which is a typical exothermic reaction, as it releases heat. Option C is the Haber process for ammonia synthesis, which is also exothermic in nature, releasing energy. Option D is incorrect because the correct endothermic reaction is given in option B.
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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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