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:

Question

Chemistry

Allan Morse

23 October, 18:36

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:

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Krista Eaton · 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