One step in the manufacture of sulfuric acid is the formation of sulfur trioxide by the combustion of SO₂ with O₂ in the presence of a vanadium(V) oxide catalyst. Suppose you are working out how to increase the equilibrium composition of sulfur trioxide. Predict how the equilibrium composition for the sulfur trioxide synthesis will tend to change when the temperature is raised.

ANTICIPATE Combustion reactions are all exothermic, so you should expect the equilibrium of this to shift in favor of reactants when the temperature is raised.

PLAN Verify that the reaction is exothermic. To find the standard reaction enthalpy, use the standard enthalpies of formation given in Appendix 2A.

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2A THERMODYNAMIC DATA AT 25 °C Inorganic Substances Substance Aluminum Al(s) Al³+ (aq) Al(OH)3(S) Al₂O3(s) AlCl3(s) AlBr,(s) Antimony Sb(s) SbH3(g) SbCl3(g) SbCls (g) Arsenic As(s), gray AsO4³ (aq) A$2S3(S) Barium Ba(s) Ba²+ (aq) BaO(s) BaCO3(s) BaCO3(aq) Molar mass, M/(g.mol-¹) 26.98 26.98 78.00 101.96 133.33 266.68 121.76 124.78 228.11 299.01 74.92 138.92 246.05 137.33 137.33 153.33 197.34 197.34 Enthalpy of formation, AH/(kJ-mol-¹) 0 -524.7 -1276 -1675.7 -704.2 -527.2 0 +145.11 -313.8 -394.34 0 -888.14 - 169.0 0 -537.64 -553.5 -1216.3 -1214.78 Gibbs free energy of formation, AG/(kJ.mol-¹) 0 -481.2 -1582.35 -628.8 0 +147.75 -301.2 -334.29 0 -648.41 -168.6 0 -560.77 -525.1 -1137.6 -1088.59 Molar heat capacity, Cr.m/J.K¹-mol¹) 24.35 79.04 91.84 100.6 25.23 41.05 76.69 121.13 24.64 116.3 28.07 47.78 85.35 Molar entropy,* Sm/(J-K¹-mol-¹) 28.33 -321.7 50.92 110.67 180.2 45.69 232.78 337.80 401.94 35.1 -162.8 163.6 62.8 +9.6 70.42 112.1 -47.3