Integrated Rate Law Calculations: 1st Order

Question

The gas phase decomposition of phosphine at 120 °C

PH₃(g)  1/4 P₄(g) + 3/2 H₂(g)

is first order in PH₃ with a rate constant of  s^-1.

If the initial concentration of PH₃ is .0514 M, the concentration of PH₃ will be _________M after  79s have passed.

Answer 1

For a first order reaction, ...

ln[A] = -kt + ln[A]o

Since you didn't include the value for k, I can't solve the equation, but you can. Just plug in k and [A]o and solve for [A] using 79s for a value of t.