The standard enthalpy of sublimation of dry ice (solid carbon dioxide) is $\Delta H=6.03\ \mathrm{kJ/mol}$. The triple point of $\ce{CO2}$ is at $p=5.1\ \mathrm{atm}$, $T=-56.7\ \mathrm{^\circ C}$.

I am trying to find the $\Delta S_\text{sublimation}$ and $\Delta G_\text{sublimation}$ at the triple point. I do not know which formula to use.

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You can work from the principle that at a phase transition the partial molar Gibbs free energy (chemical potential) of the substance in each phase is equal, so that

$$\Delta_\mathrm{sub} G = 0$$

from which

$$\Delta_\mathrm{sub} S_\mathrm{m} = \frac{\Delta_\mathrm{sub} H_\mathrm{m}}{T_\mathrm{sub}}$$

Note however that the value of $\Delta_\mathrm{sub} H_\mathrm{m}$ that you provide seems a bit off$^\dagger$. NIST gives a value at $\pu{207 K}$ of $\Delta_\mathrm{sub} H_\mathrm{m} = \pu{26.1 kJmol^{-1}}$. Values at other temperatures in the range $\pu{167-195 K}$ are similar. Other internet sources can helpfully confirm this.

$\dagger$ The value you post may be in $\pu{kcal mol-1}$, then it would translate into $\pu{25.3 kJ mol-1}$, in reasonable agreement with the values on the NIST data page.


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