The gas-phase reaction is extremely slow at

CHEMISTRY · Multi-part · A Level · Chemistry · Kinetics · Kinetics

Problem

The gas-phase reaction CO+NO→CO2+12 N2\mathrm{CO} + \mathrm{NO} \rightarrow \mathrm{CO}_2 + \frac{1}{2}\,\mathrm{N}_2 is extremely slow at 500 K500\,\text{K}. In an automotive catalytic converter, the reaction proceeds rapidly on a platinum surface. A simplified data set is shown below. Uncatalyzed reaction in the gas phase at 500 K500\,\text{K}: activation energy Ea=200 kJ mol−1E_{\mathrm{a}} = 200\,\text{kJ mol}^{-1}. Catalyzed reaction on Pt at 500 K500\,\text{K}: activation energy Ea′=120 kJ mol−1E_{\mathrm{a}}' = 120\,\text{kJ mol}^{-1}. Assume the pre-exponential factor AA is unchanged by the catalyst. (a) Describe qualitatively how adsorption of CO and NO onto a platinum surface can alter the reaction mechanism compared with the homogeneous gas-phase pathway. (b) Sketch a qualitative potential-energy diagram (no numeric scale required) that compares the uncatalyzed and Pt-catalyzed pathways. Clearly label the activated complex(es), reaction intermediates (if any), and relative activation energies. (c) Using the Arrhenius equation, calculate the factor by which the rate constant increases at 500 K500\,\text{K} when the reaction is performed on platinum rather than in the gas phase. Use R=8.314 J mol−1 K−1R = 8.314\,\text{J mol}^{-1}\,\text{K}^{-1} and express your answer to two significant figures.

Related theory

Browse the problem library