In a generic chemical reaction involving reactants A and B and products C and D, aA + bB → cC + dD, the standard enthalpy ΔH°rxn of the reaction is given by ΔH°rxn = cΔH°f(C) + dΔH°f(D) - aΔH°f(A) - bΔH°f(B). Notice that the stoichiometric coefficients, a, b, c, and d, are an important part of this equation. This formula is often generalized as follows, where the first sum on the right-hand side of the equation is a sum over the products and the second sum is over the reactants: ΔH°rxn = ∑products nΔH°f - ∑reactants mΔH°f, where m and n represent the appropriate stoichiometric coefficients for each substance.
Part A
What is ΔH°rxn for the following chemical reaction?
CO(g) + NH3(g) → HCN(g) + H2O(g)
You can use the following table of standard heats of formation (ΔH°f) to calculate the enthalpy of the given reaction.
Element/Compound Standard Heat of Formation (kJ/mol)
H(g) 218
N(g) 473
H2(g) 0
O2(g) 0
NH3(g) -45.90
O(g) 249
CO(g) -110.5
H2O(g) -241.8 kJ
C(g) 71
HCN(g) 130.5 kJ
C(s) 0
HNO3(aq) -206.6
Express the standard enthalpy of reaction to three significant figures and include the appropriate units.
