The rate of appearance

Question

2A + B > C+D 

the rate of disappearance of A in the reaction above is -d[A]/dt = K[A][B]2

what happens to the rate of appearance of C if the concentration of A is doubled and that of B is tripled

Answer 1

The rates of the various constituents of a reaction equal each other when dividing each rate by its stoichiometric constant.  Therefore,

 

d[C]/dt = -(0.5)d[A]/dt

 

In this problem you don't care about the quantitative measurement of the rates, but rather the qualitative ratios. Thus, you can disregard the stoichiometric constant and simply take the ratio of d[A]/dt before and after carrying out the changes in concentration:

 

ratio = {K[2A][3B]^2}/{K[A][B]} = 18

 

thus, the rate increases by a factor of 18.