What is the enthalpy of formation of NO2 (g) at 1298K?
Correct answer: C. - 45 kJ/mol
- A. - 40 kJ/mol
- B. -50 kJ/mol
- C. - 45 kJ/mol
- D. - 6 kJ/mol
Explanation
The enthalpy of formation of a compound is the heat change that results when one mole of the compound is formed from its elements in their standard states. For NO₂, this value is determined experimentally and is known to be approximately -45 kJ/mol at 1298K.ΔH(1298) = ΔH(298) + (ΔCp × ΔT) ΔH(1298) = -40,000 J + (-5 × 1000) ΔH(1298) = -40,000 - 5,000 = -45,000 J ΔH(1298) = -45 kJ/mol
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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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