Dry ice (solid ) can either melt to liquid or sublime directly to gaseous

CHEMISTRY · Multi-part · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

Dry ice (solid

\mathrm{CO}_2

) can either melt to liquid

\mathrm{CO}_2

or sublime directly to gaseous

\mathrm{CO}_2

, depending on the pressure conditions. Consider the following phase changes at

194\,\text{K}

, the triple-point temperature of

\mathrm{CO}_2

. Process I:

\mathrm{CO}_2(\mathrm{s}) \rightarrow \mathrm{CO}_2(\ell)

Process II:

\mathrm{CO}_2(\mathrm{s}) \rightarrow \mathrm{CO}_2(\text{g})

(1) (a) Predict and justify the sign of

\Delta S^\circ

for Process I. (2) (a) Predict and justify the sign of

\Delta S^\circ

for Process II. (3) (b) Compare

|\Delta S^\circ|

for the two processes and explain the difference. (4) (c) Connect your entropy analysis to the practical use of

\mathrm{CO}_2

sublimation in refrigeration.