Question

Estimate the value of the equilibrium constant at 640 K for each of the following reactions. ΔH∘fand S∘ for BrCl(g) is 14.6 kJ/mol and 240.0 Jmol⋅K, respectively.

Part A

2NO2(g)⇌N2O4(g)

Part B

Br2(g)+Cl2(g)⇌2BrCl(g)

Express your answer using two significant figures.

Answer 1

To calculate this, you are missing the data for Part A, so I'm gonna solve Part B, so you can have an idea.

The reaction is as follow:
Br_2(g) + Cl_2(g) --------> 2BrCl_(g)

To get K, we can use the following expression:
= -RTlnK
K = exp(-/RT)

And to get :
= H - TS

So in order to solve this and Part a) we need the H and S of the reactions, and then, the Kc.

For Hrxn = Hprod - Hreact
Hrxn = (14.6*2) - 0 = 29.2 kJ/mol

To get S, we do the same thing:
S = Sprod - Sreact
S = (2*240) - (222.96 + 245.35) = 11.69 J/mol K

G = 29200 - 640*11.69 = 21718.4 J/mol or 21.72 kJ/mol

Finally K:
K = exp (-21718.4 / 8.3144*640)
K = 0.01688

With the missing data of the compounds in part a) use the same procedure as here. Hope this helps