Assume the rate of disappearance of PH3 is 2.5 x 10^-3 M/s at 20 seconds.

Question

4PH3 (g) ➞ P4 (g) + 6H2 (g)

a. What is the rate of appearance of P4 at 20 seconds?

b. How will the rate of P4 appearance change (qualitatively) as the reaction

progresses?

Justify each answer!

Answer 1

(a). rate of appearance of P4 @ 20 sec = 1/4 x 2.5x10^-3 M/s = 6.25x10^-4 M/s

(b). As the reaction progresses, the rate of appearance of P4 will decrease.

Justification of this response is that as the reaction progresses, the concentration of the reactant PH₃ is decreasing and the rate of reaction is dependent on the concentration of reactant (assuming non zero order). Thus as it decreases, the rate of reaction decreases, and thus rate of appearance of P4 decreases over time,