calculate k?

Question

Given the following:

A --> 1/2B + C, K= 0.0334
3D --> B + 2C, K = 2.35

Calculate K for: 2A -> 3D

Here's my work..

I basically multiplied the first equation by 2 and flipped the second equation to get 2A -> 3D.

How would I calculate K now?

Answer 1

If you define K for the first reaction as K1 and for the second as K2, then K for 2A ---> 3D will be:

K = K1^2 / K2

If you multiply a reaction by 2, then you will square the equilbrium constant. Reversing a reaction means the equilbrium constant is the inverse of the original, so when adding the expressions together, you mutiply the equilibrium constants, thus it will be the same as dividing by K2.

So K for your final reaction will be:

(0.0334)^2 / 2.35 = 4.75 * 10^-4

Answer 2

don't use substitution it will be too hard
try elimination

you're algebra book should tell you how to do it