Question

Calculate the enthalpy change for the following reaction using Hess's Law: 2SO3(g) → 2SO2(g) + O2(g)Given the following enthalpy changes:2SO3(g) + ΔH1 → 2SO2(g) + O2(g); ΔH1 = 198.2 kJ/molSO2(g) + 1/2O2(g) + ΔH2 → SO3(g); ΔH2 = -98.9 kJ/mol

Answer 1

To calculate the enthalpy change for the given reaction using Hess's Law, we need to manipulate the given reactions and their enthalpy changes to match the target reaction.Target reaction: 2SO3 g   2SO2 g  + O2 g Given reactions:1  2SO3 g  + H1  2SO2 g  + O2 g ; H1 = 198.2 kJ/mol2  SO2 g  + 1/2O2 g  + H2  SO3 g ; H2 = -98.9 kJ/molFirst, we need to reverse the second reaction to match the target reaction:2'  SO3 g   SO2 g  + 1/2O2 g ; H2' = 98.9 kJ/molNow, we need to multiply the second reaction by 2 to match the target reaction:2''  2SO3 g   2SO2 g  + O2 g ; H2'' = 2 * 98.9 kJ/mol = 197.8 kJ/molNow, we can add the reactions to get the target reaction:1  2SO3 g   2SO2 g  + O2 g ; H1 = 198.2 kJ/mol2''  2SO3 g   2SO2 g  + O2 g ; H2'' = 197.8 kJ/molThe enthalpy change for the target reaction is the sum of the enthalpy changes of the manipulated reactions:H = H1 + H2'' = 198.2 kJ/mol + 197.8 kJ/mol = 396 kJ/molSo, the enthalpy change for the reaction 2SO3 g   2SO2 g  + O2 g  is 396 kJ/mol.