## Molar internal energy (4B.3A) [ENDORSED]

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

Malia Shitabata 1F
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### Molar internal energy (4B.3A)

Can someone walk me through this problem? I'm not sure I understand molar internal energy properly because I'm not getting the right answer when I plug it in:

Estimate the contribution of motion to the molar internal energy of water vapor at 25 ºC.

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### Re: Molar internal energy (4B.3A)  [ENDORSED]

The contribution of motion to the molar internal energy of a water molecule at 25C is the sum of its average rotational and translational energies at that temperature. As described in the passage above the problem, the translational energy is 1.5RT and the rotational energy for a nonlinear molecule (water is bent and therefore nonlinear) is 1.5RT. Added together this is 3RT= 3 * 8.314 J/ mol K * (273 + 25)K = 7.44 kJ/mol

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