Question

Given the following general reaction:
A + 2B + 3C -> P + 4Q.
Show how the change in concentration of C with time is related to the change in concentration of A, B, P, and Q with time.

Answer 1

C changes three times as fast as A, 1.5 times as fast as B, and C also changes three times fast as P (but in the opposite direction).

Answer 2

Remember, these type kinetics problems are always based upon ‘pairs’ of substances. A quick setup is to equate the rates of the two substances of interest and switch the coefficients. One of the rates will be given. Solve for the unknown in terms of the given rate value. For this problem…
A + 2B + 3C => P + 4Q
1 (∆[C])/∆t=3 ([∆A])/([∆t])
2 (∆[C])/∆t=3 ([∆B])/([∆t])
1 (∆[C])/∆t=3 ([∆P])/([∆t])
4 (∆[C])/∆t=3 ([∆Q])/([∆t])