(a) What is the entropy of a perfect crystal at 0 $\mathrm{K}$ ?

(b) Does entropy increase or decrease as the temperature rises?

(c) Why is $\Delta H_{\mathrm{f}}^{\circ}=0$ but $S^{\circ}>0$ for an element?

(d) Why does Appendix $\mathrm{B}$ list $\Delta H_{\mathrm{f}}^{\circ}$ values but not $\Delta S_{\mathrm{f}}^{\circ}$ values?

## Discussion

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