If the reaction is begun with an initial PH3 concentration of 0.95 M, what will be the concentration of PH3 after 36.50 s?

Question

The rate of decomposition of PH₃ was studied at 961.00 °C. The rate constant was found to be 0.0815  s^–1.

4PH₃ --> P₄ + 6H₂

If the reaction is begun with an initial PH₃ concentration of 0.95 M, what will be the concentration of PH₃ after 36.50  s?

Answer 1

Based on the units for the rate constant (s^-1), we can tell the reaction is FIRST ORDER. The rate equation for a first order reaction is

ln[A]_t = ln[A]_o - kt

ln[A]_t = ln 0.95 - 0.0815*36.50

ln[A]_t = -0.0513 - 2.97 = -3.03

[A]_t = 0.0485M

Please check all math.