Self-test 5H.2A

[Danielle_Cho_3A]

Hello,

I was trying to do Self-test 5H.2A, but I was not sure how to get started on solving this problem. Are we supposed to convert from Kp to Kc?
The answer says (delta)n(sub r) is -2, but how do we use this value?

[Jessa 2K]

Yes, you have to convert to Kc from Kp. The formula for the conversion is Kp = Kc(RT)^dn (n = mole coefficient of products - mole coefficient of reactants).
The chemical formula for the synthesis of ammonia is N2 + 3H2 --> 2NH3. So we need to know n, which is 2 mol coefficients on product side - 4 mole coefficients on reactants side, which equals -2. I converted 127 C to 400 Kelvin, and used 0.0825 for constant R. Then I plugged in all the numbers:
41 = Kc[0.08205 (L x atm)/(mol x K) x 400K)^-2]
And I got 4.5 x 10^4
Hope this helps