7. Given the following rate law, how does the rate of reaction change if the concentration of Y is reduced by a factor of three? Rate = k [X] [Y]2

Answer 1

rate = k[X][y]²

This tells us the rate varies directly with [X] and to the square of the [Y]. If the [Y] is reduced by a factor of 3, the rate should decrease by a factor of 9, i.e. 3².

To check this, let us set k = 1 for simplicity. We will also set [x] = 1 and [Y] = 1 for the first experiment.

rate = (1)(1)(1)² = 1

Now, set [Y] = 0.333, i.e. reduced by a factor of 3 and solve for rate.

rate = (1)(1)(0.333)² = 0.110

1/0.110 = 9.0 so in fact the rate was reduced by a factor of 9 as predicted above.