Question

The thermal decomposition of phosphine (ph3) into phosphorus and molecular hydrogen is a first-order reaction: 4ph3(g) → p(g) + 6h2(g) the half-life of the reaction is 35.0 s at 680°c. calculate the first-order rate constant for the reaction:

Answer 1

if we need to get K ( the first order constant rate ) and when we have
t(1/2) = 35 s as a given so we will use this formula:

t(1/2) = ㏑2 / K
by substitution:
35 = (0.693) / K
∴ K = (0.693) / 35
= 0.0198 s^-1