An energy diagram for the gas-phase combustion of CO(g) to form CO₂(g) at 298 K indicates ΔHrxn=–281kJ mol−1. To assess the accuracy of the diagram, a student consults a table of standard molar enthalpies of formation, reproduced below.
Species
ΔHf∘ (kJ mol⁻¹)
CO(g)
–110.5
CO₂(g)
–393.5
O₂(g)
0
The balanced chemical equation is:
2 CO(g) + O₂(g) → 2 CO₂(g)
Assume all species are in their standard states.
(a) Use the tabulated data to calculate ΔHrxn∘ for the combustion of one mole of CO(g). Show your work clearly.
(b) Compare your calculated value with the enthalpy change reported on the energy diagram. Quantitatively evaluate whether the diagram is thermodynamically consistent. State any percentage difference you compute to support your conclusion.
(c) If the energy diagram were to be redrawn to align exactly with standard enthalpy data, indicate how the vertical positions of reactants, products, and the transition state would need to shift. Provide numerical adjustments relative to the original diagram.