Question #44072

Consider the elementary reversible dimerization of nitrogen dioxide in a cylinder fitted with a frictionless, movable piston at $298\text{ K}$ (assume ideal gas behavior): $2\ce{NO2(g)} \rightleftharpoons \ce{N2O4(g)}$ The system is initially at chemical equilibrium with forward rate $r_f$ and backward rate $r_b$. An inert gas ($\ce{He}$) is injected isothermally and isobarically, increasing the total volume of the system by a factor of $\alpha$ ($\alpha > 1$). Let $r_f'$ and $r_b'$ be the instantaneous rates immediately after the injection (prior to any chemical relaxation). Which of the following correctly represents the ratio $\frac{r_f'}{r_b'}$ and the direction of the subsequent thermodynamic shift?