## 4G.5

Boltzmann Equation for Entropy: $S = k_{B} \ln W$

Junwei Sun 4I
Posts: 125
Joined: Wed Oct 02, 2019 12:16 am

### 4G.5

The question is:

Considering positional order, would you expect a crystal of octahedral cis-MX2Y4 to have the same, higher, or lower residual entropy than the corresponding trans isomer? Explain your conclusion.

The solution manual says that cis-MX2Y4 has 12 orientations whereas the trans isomer only has 3 and that's the part that I don't understand. Could someone please explain why there are 12 orientations? Thanks!

Connie Chen 1E
Posts: 51
Joined: Mon Jun 17, 2019 7:24 am

### Re: 4G.5

There are 12 orientations because in a cis- isomer, the X's must be adjacent to each other, or 90 degrees from each other in this case. With the octahedral cis-MX2Y4, there are 12 different ways for the two X's to be next to each other.

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