Le Chatelier violating kinetics?

Question

For the reaction below: CO2(g) + 3H2(g) CH3OH(l) + H2O (l), ∂H=-40kj/mol What happens to the rate of the reaction if we heat this up? Normally I'd say the reaction rate increases just by looking at the Arrhenius equation. But doesn't Le Chatelier tell us that for an exothermic reaction (like this one), adding heat will push us back toward the products (and therefore decrease reaction rate)? Thanks, guys!

Answer 1

Conrad, there is an important distinction to make here between kinetics and equilibrium. While raising temperature will cause the rate of the forward reaction to increase (by increasing the number of collisions that have more kinetic energy than the activation energy), it will also cause the rate of the reverse reaction to increase. Remember that equilibrium is the point at which the forward and reverse rates are equal, so we can see that if the rates of the forward and reverse reactions increase by different amounts, we can move the equilibrium either way, dependent upon the enthalpy of the reaction.

Let me know if you have any more questions and we can set up a tutoring session.