Ho of which of the following reactions is equal to the standard enthalpy of formation of NH3?
Correct answer: A. 3H2(g) + N2(g) → 2NH3(g)
- A. 3H2(g) + N2(g) → 2NH3(g)
- B. 2NH3(g) → 3H2(g) + N2(g)
- C. 3/2 H2(g) + 1/2 N2(g) → NH3(g)
- D. NH3(g) → 3/2 H2(g) + 1/2 N2(g)
Explanation
The standard enthalpy of formation (ΔH°f) of a compound is the enthalpy change when one mole of the compound is formed from its constituent elements in their standard states, with all reactants and products in their standard states at a specified temperature (usually 25°C) and pressure (usually 1 atm).The standard enthalpy of formation of NH3 (ammonia) is -46.1 kJ/mol.To find the reaction whose standard enthalpy change (ΔH°) is equal to the standard enthalpy of formation of NH3, we look for the reaction that forms NH3 from its constituent elements (N2 and H2) in their standard states.The correct reaction is: 3H2(g) + N2(g) → 2NH3(g)
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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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