Consider the reversible unimolecular reaction:

$$\ce{A <=>[k_1][k_2] B}$$

We know that the forward reaction is often considerably more thermodynamically favourable than the reverse reaction, and therefore the relationship $k_1 \gg k_2$ holds between the rate constants. The rate constants are in the same units, and so it is possible to write this relationship. A similar example would be a reaction that is bimolecular on both sides, $\ce{A + B <=> C + D}$, etc.

However, consider this reversible reaction:

$$\ce{A + B <=>[k_1][k_2] C}$$

Assume the reaction proceeds at rate $k_1 [\ce{A}][\ce{B}]$ in the forward direction and $k_2 [\ce{C}]$ in reverse. If the overall reaction rate has units $M s^{-1}$, then $k_1$ necessarily has units $M^{-1} s^{-1}$ and $k_2$ has units $s^{-1}$.

**My question is:** For this second case, we can no longer impose that $k_1 \gg k_2$, due to difference in units, but can we say *anything* about their relationship? Does setting $k_1$ to some value constrain the choice of $k_2$ in any way?