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A-Level Enthalpy, entropy and the feasibility of reactions: worked solution
2 marks. Full working, one step per line.
Question
Take the equilibrium: N2 (g) + 3H2 (g) ⇌ 2NH3 (g). Suppose the ammonia formed were a liquid rather than a gas. State, with an explanation, how this would change the value of ΔH° for the reaction.
Worked answer
Condensing gaseous ammonia to liquid ammonia is an exothermic process (it releases the enthalpy of vaporisation/condensation). If the product were formed as a liquid rather than a gas, this extra energy would be released in addition to the energy already given out. Therefore Delta H would become more exothermic, i.e. more negative (by about 2 times the molar enthalpy of condensation of NH3, since 2 mol of NH3 are formed).
Practise this topic
This question is part of A-Level Enthalpy, entropy and the feasibility of reactions, in A-Level H2 Chemistry.
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