Question

For the reaction A+B+C→D+E, the initial reaction rate was measured for various initial concentrations of reactants. The following data were collected:

Trial [A] (M) [B] (M) [C] (M) Initial rate (M/s)

1 0.30 0.30 0.30 9.0×10−5

2 0.30 0.30 0.90 2.7×10−4

3 0.60 0.30 0.30 3.6×10−4

4 0.60 0.60 0.30 3.6×10−4

Answer 1

We can do this in two ways. I'll do it by both ways.

In the first way you can simly use the equation:

r = -dA / dt and solve the values for the concentration of the product and time so:

r = 7.60x10^-3 - 1x10^-3 / 40-10 = 2x10^-4 M/s

However, as the question is an average rate, then, we should do it by the second way, take time intervals, first between 10 and 20, 20 and 30, 30 and 40, and at the end, we'll take the average of those values, and then, compare to the previously obtained:

r₁ = 4x10^-3 - 1x10^-3 / 20-10 = 3x10^-4 M/s

r₂ = 5.8x10^-3 - 4x10^-3 / 30-20 = 1.8x10^-4 M/s

r₃ = 7x10^-3 - 5.8x10^-3 / 40-30 = 1.2x10^-4 M/s

r = (3+1.8+1.2)x10^-4 / 3 = 2x10^-4 M/s

Both results are the same, so this would be the correct way to follow.

Hope this helps