[Squeak1107]

Two products, C and D are produced by the following competing reactions:
A+B→C
A+B→D
The two competing reactions have the same order of reaction with respect to both A and B.

(ii) Write an expression showing how you would expect the ratio of the product concentrations, [C]/[D] to vary with temperature if the activation energy for the reaction producing D is 25% greater than that of the reaction producing C.

What I have tried so far is to use the arrhenius equation to get
lnk_d = luna - 1.25E_a/RT and lnk_c = lnB - E_a/RT.
I then get lnk_d - luna = 1.25(lnk_c - 1.25lnB)

I'm not too sure where to go from here though as I have no term for concentration in this expression. Any help would be appreciated!

[Corribus]

You don't need specific concentrations because everything is relative. If you call the rate of the first reaction k₁ and the rate of the second reaction k₂, try expressing k₂ in terms of k₁. If you know [D] forms x times as fast as [C] at temperature t, it is straightforward to express this as a ratio of [D]/[C].