Question

What is the value of the equilibrium constant at 655 K for each of the following reactions?

`2NO_2(g)harrN_2O_4(g)`
`Br_2(g)+Cl_2(g)harr2BrCl(g)`

I figured out how to calculate `DeltaG^0` using `DeltaH^0` and `DeltaS^0`, but I am unable to determine the value for `DeltaG` because it is not at STP. Do I just plug in `DeltaG^0` to the `-RTlnK` equation to find the value of K, or do I have to adjust something for its not being at STP?

Answer 1

`K approx 1.67`

Explanation:

Yes! You're correct, I'll do the first one.

`2NO_2(g) rightleftharpoons N_2O_4(g)`

`DeltaG^0 approx -2.8kJ`

I did that per the usual method using a table in my text.

`-2.8*10^3 J = -(8.314J)/(mol*K)* (655K) * lnK`
`therefore K approx 1.67`

This is reasonable because, I did a quick check and noticed this reaction has favorable enthalpy but unfavorable entropy. Thus, it will be nonspontaneous at high temperatures. Thus, not much product will form relative to standard conditions.