A catalytic converter promotes the reaction
CO(g)+21O2(g)⟶CO2(g)
Inside the converter, the reaction proceeds through an adsorbed complex in which the C–O bond in CO weakens before a new C=O bond forms to produce CO2. Assume the overall transformation can be modeled in a single energetic step for calculation purposes.
Average gas-phase bond energies (kJ mol−1): C≡O (in CO) 1072, O=O 498, C=O (in CO2) 799.
Because the reaction occurs on a catalyst surface, the effective C≡O bond energy in adsorbed CO is reduced by approximately 160 kJ mol−1 relative to the gas-phase value.
(a) Using the adjusted bond energy for adsorbed CO, calculate the enthalpy change, ΔHrxn, for the catalytic conversion on a per-mole basis as written.
(b) The uncatalyzed gas-phase reaction has ΔHrxn=−283kJ mol−1. Compare this value with your result from part (a) and discuss the thermodynamic effect, if any, of adsorption on ΔHrxn.
(c) Sketch a qualitative energy diagram for both the gas-phase and surface-catalyzed reactions on the same axes, indicating reactants, products, activation energy, and ΔHrxn for each pathway.
(d) Explain how the modification of the C≡O bond energy upon adsorption can alter the activation energy without significantly changing the overall ΔHrxn, and relate this to the role of the catalyst.