Question

Calculate the enthalpy change for the isomerization of butene to isobutene given that the enthalpy of combustion for butene is -2671.2 kJ/mol and the enthalpy of combustion for isobutene is -2678.6 kJ/mol. Assume that the molar enthalpy of formation of CO2 and H2O are -393.5 kJ/mol and -241.8 kJ/mol, respectively.

Answer 1

To calculate the enthalpy change for the isomerization of butene to isobutene, we can use Hess's Law. Hess's Law states that the enthalpy change for a reaction is the same whether it occurs in one step or several steps. In this case, we can use the enthalpy of combustion for butene and isobutene to determine the enthalpy change for the isomerization.First, let's write the balanced combustion reactions for butene and isobutene:Butene:C4H8  g  + 6 O2  g   4 CO2  g  + 4 H2O  l   H_combustion = -2671.2 kJ/molIsobutene:C4H8  g  + 6 O2  g   4 CO2  g  + 4 H2O  l   H_combustion = -2678.6 kJ/molNow, we can use Hess's Law to determine the enthalpy change for the isomerization of butene to isobutene:H_isomerization = H_combustion  isobutene  - H_combustion  butene H_isomerization =  -2678.6 kJ/mol  -  -2671.2 kJ/mol H_isomerization = -7.4 kJ/molThe enthalpy change for the isomerization of butene to isobutene is -7.4 kJ/mol.