The gaseous phase reaction $\mathrm{A}\left(\mathrm{g}\right)\to 2 \mathrm{B}( \mathrm{g})+\mathrm{C}\left(\mathrm{g}\right)$ is first order with respect to A. If the reaction is started with pressure${\mathrm{p}}_0$ of A, then the pressure ${\mathrm{p}}_{\mathrm{t}}$ of the system at time$\mathit{ }t\mathit{ }$is given by the expression