A student wants to calculate the standard enthalpy change for the synthesis of ammonia, represented by the balanced chemical equation
N2(g)+3H2(g)→2NH3(g).
Standard enthalpies of formation for all species are available in a reference table.
(a) Describe the procedure the student should follow to obtain the standard enthalpy change for the reaction using only the tabulated standard enthalpies of formation for the reactants and products.
(b) Explain why the numerical value obtained in part (a) must be divided by two if the student wishes to report the enthalpy change per mole of NH3(g) produced.
(c) The student mistakenly omits the stoichiometric coefficient on H2(g) when combining the formation data. Predict qualitatively (more negative, less negative, or unchanged) how this error will affect the calculated enthalpy change and justify your prediction.