What will be the enthalpy change in the reaction given below?2H2 + O2→ 2H2O ∆H = +205.5 kJ mol-1
Correct answer: C. -205.5 kJ/mol
- A. 205.5 kJ/mol
- B. Zero kJ/mol
- C. -205.5 kJ/mol
- D. 1 kJ/mol
Explanation
This is a trick question. Most students choose A however that is wrong. It should be remembered that ∆H for combustion is an exothermic process and energy is released thus option C is correct. It is a fact.
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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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