The integrated rate law equation for a first-order gas-phase reaction $A(g) \rightarrow B(g) + C(g)$ is given by (where $P_i$ is the initial pressure and $P_t$ is the total pressure at time $t$):

• A
  $k = \frac{2.303}{t} \log \frac{P_i}{2 P_i - P_t}$
• B
  $k = \frac{2.303}{t} \log \frac{2 P_i}{2 P_i - P_t}$
• C
  $k = \frac{2.303}{t} \log \frac{2 P_i - P_t}{P_i}$
• D
  $k = \frac{2.303}{t} \times \frac{P_i}{2 P_i - P_t}$