Question

The reaction X + Y --> products was studied using the method of initial rates. The initial rate of consumption of X was measured in three different experiments. What is the value of the rate constant, k?

*concentrations are in mol/L and initial rates are in molL-1s-1
Exp 1:
[X]initial=0.6
[Y]initial=0.6
Initial Rate=3.306
Exp 2:
[X]initial=1.2
[Y]initial=0.6
Initial Rate=1.653
Exp 3:
[X]initial=0.6
[Y]initial=1.8
Initial Rate=29.75

My first step was to determine the rate law. However, I got r=k[X]^-1[Y]^2
I check this over numerous times and don't know what I'm doing wrong because you can't have a negative exponent in a rate law.. can you?!

Answer 1

In general, the orders (exponents) in a rate law can turn out to be positive or negative rational numbers, so -1 is a possibility.