Equilibrium: extent of chemical reactions

Question

hey,

I cant figure out how to solve this, anyone who can help me with a youtube video?

At a particular temperature, K_c = 1.6x10^-2 for

2H₂S -><- 2H₂ + S₂

Calculate K_c for the following reaction:

5H₂S -><- 5H₂ + 5/2S₂

Thanks a lot!

Answer 1

Don't have a youtube video, but will work it out and hope you understand it.

2H₂S <==> 2H₂ + S₂ and the Kc for this reaction is 1.6x10^-2

The reaction of interest is 5H₂S <==> 5H₂ + 5/2 S₂ which is 2.5 times (or 5/2) the original reaction, right?

Well, when you multiply a reaction by a factor (in this case, by 5/2 or 2.5), you have to raise the original Kc value to that same value. Example: A => B and K = 1x10^-2. For 2A => 2B, K = (1x10^-2)² = 1x10^-4.

So, for the current problem, to find the Kc for the new reaction we need to raise the Kc of the original reaction to the 2.5 power.

Kc for the new reaction = (1.6x10^-2)^2.5 = 3.2x10^-5

Extra notes:

If you were to divide the original equation by 2, the new Kc would be the square root of the original Kc

If you were to reverse the reaction, the new Kc would be the inverse of the original Kc