Rate \(=\mathrm{k}\left[\mathrm{PH}_{3}\right]\)
It is dependent on surface coverage because at low pressure, surface area covered is proportional to partial pressure
of \(\mathrm{PH}_{3}\) and it is first order w.t.t. \(\mathrm{PH}_{3}\)
\(\theta=\frac{k P}{1+k P}\)
\(\theta=\) fraction of surface area covered at low pressure \(\theta=\mathrm{k} \mathrm{P}\)

(આપેલ : $\ln 2=0.693)$
(આપેલું છે$: \ln 10=2.3, R =8.3 \,J\, K ^{-1} \,mol ^{-1}, \log 2=0.30$ )