[klee256]

Arsine's vapor P is 35 Torr at -111.95°C and 253 Torr at -83.6°C. Using only this data, calculate the standard entropy of vaporization.
I found the standard enthalpy of vaporization with the Clausius-Clapeyron equation, but I don't get how to find this. I'm pretty sure I just have to plug in the numbers in one of the following (below), but I don't know which one is right.
There's an equation in the derivation of the Clausius-Clapeyron equation that states ln(P/P°) = -ΔG_vap°/RT, but I've found another equation that says ln(P) = -ΔG_vap°/RT. Which one is right?

[mjc123]

Both. Technically it should be the ln(P/P°) one, because P needs to be referenced to the standard pressure P°. But P° is usually 1 atm, so it is often omitted, as in the second equation. But if you are using pressure units in which the value of P° is not 1, you need to include it.

[Enthalpy]

Is it G or H?

You could memorize instead something like
P is proportional to exp(-H/RT) because it resembles a distribution hence costs no additional memory effort.

Consistency of the units should tell you where there is a ratio of pressures, or possibly where a pressure reference is implicit (a bad practice leading to errors). You take the Log(), sin(), exp() of numbers without dimension (which includes angles), not of a pressure or a temperature. So E/RT is a good candidate in an exp() while P alone is a bad one in a Log(), suggesting an implicit P₀ or a P₂/P₁.

Alas, implicit references are frequent in thermodynamics, and when a Log is involved (notably in the entropy) it can become an additive constant, more difficult to track. Sometimes the bad habit is generalized, like the noise power density as dB/sqrt(Hz) in electrical engineering, a unit that makes formally no sense.

[mjc123]

Is it G or H?

G in the equation quoted, which is a form of equilibrium constant equation. H in the Clausius-Clapeyron equation which gives the T-dependence:
d(lnP)/dT = ΔH_vap°/RT²