For this first-order isomerization reaction, ${\mathrm{CH}}_3\mathrm{NC}⟶{\mathrm{CH}}_3\mathrm{CN}$, how do the properties of the reaction in the table below vary as the reaction proceeds?

Rate of reaction $-\frac{\mathrm{\Delta }\left[{\mathrm{CH}}_3\mathbf{NC}\mathbf{]}\right.}{\mathrm{\Delta }t},\left(\mathbf{M}\cdot {\mathbf{8}}^{-1}\right)$	Half-life, (s)
(P) remains the same	decreases
(Q) decreases	remains the same
(R) remains the same	remains the same
(S) decreases	decreases