Chem 30
Calculating ∆H from Standard Heats of Formation
1. Methane, the major component of natural gas, is used as a source of hydrogen gas to
produce ammonia. Ammonia is used as a fertilizer and a refrigerant, and is used to
manufacture fertilizers, plastics, cleaning agents, and prescription drugs. The
following questions refer to some of the chemical reactions of these processes.
a. The first step in the production of ammonia is the reaction of methane with steam
using a nickel catalyst. Calculate the ∆H for the following reaction as written.
CH4(g) + H2O(g) → CO(g) + 3 H2(g)
b. The second step of this process is the further reaction of carbon monoxide to
produce more hydrogen. Both iron and zinc-copper catalysts are used. Calculate
the ∆H for the following reaction as written.
CO (g) + H2O(g) → CO2(g) + H2(g)
c. After the carbon dioxide gas is removed by dissolving it in water, the hydrogen
reacts with nitrogen obtained from the air. Calculate the ∆H for the formation of
two moles of ammonia.
2. Nitric acid, required in the production of nitrate fertilizers, is produced from ammonia
by the Ostwald process. Predict the standard enthalpy change for each reaction in the
process, as written, and then predict the standard molar enthalpy of reaction for the
first reactant listed in each equation.
a. 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g)
b. 2 NO(g) + O2(g) → 2 NO2(g)
c. 3 NO2(g) + H2O(l) → 2 HNO3(l) + NO(g)
3. Ammonium nitrate fertilizer is produced by the reaction of ammonia with nitric acid
resulting from the series of reactions given in question 2. Ammonium nitrate is one
of the most important fertilizers for increasing crop yields.
a. Predict the standard enthalpy change of the reaction used to produce ammonium
nitrate.
NH3(g) + HNO3(l) → NH4NO3(s)
b. Sketch a potential energy diagram for the reaction in part a.