constant expression for the reduction of NO with H2
with a second-power dependence on H2
concentration in the denominator.
The reason for the apparent contradiction
between this equilibrium-constant expression and the rate
law is that any complications of mechanism that affect the forward
reaction and its rate law also affect the reverse reaction in the
same way. They both cancel out in the overall equilibrium-constant
Although the correct rate law for the
forward or reverse reaction cannot be deduced from the balanced
reaction alone, the equilibrium-constant expression can be.
A classical example of complications in a
rate expression is the reaction analogous to HI production, but with
bromine instead of iodine:
The equilibrium-constant expression is: