Does an object lose a little bit of energy during a phase change, such as when an ice cube melts and expands? When the object expands, it does work on the surrounding air particles, but does this imply a loss of internal energy?
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1$\begingroup$ what makes you think an ice cube expands when it melts? See the section "what's going on" in the following link:exploratorium.edu/snacks/melting-ice-rising-seas $\endgroup$– Bob DCommented Jun 7, 2023 at 15:28
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2$\begingroup$ But, in general, yes. The PV work is part of the Gibbs free energy terms. Since the volume changes in a first order phase transition, pressure effects the temperature at which it will occur. $\endgroup$– Jon CusterCommented Jun 7, 2023 at 15:34
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$\begingroup$ Got it. Thank you! $\endgroup$– Authentic MelodyCommented Jun 7, 2023 at 16:12
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$\begingroup$ @JonCuster What PV work is involved here? $\endgroup$– Bob DCommented Jun 7, 2023 at 17:59
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$\begingroup$ @BobD - since there is a volume change at some ambient pressure, fine phase is preferred over another. That is, the phase transition temperature changes with ambient pressure. Looking at a PV diagram for an element tells you which of the liquid or solid is higher density based on the slope of the phase boundary. All part of the relative Gibbs free energy of the phases. $\endgroup$– Jon CusterCommented Jun 7, 2023 at 20:20
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1 Answer
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An ice cube doesn't expand when it melts. An ice cube is less dense than water. Therefore its volume will be less after it melts, not more. So there is no expansion work involved when ice melts.
See the section "what's going on" in the following link https://www.exploratorium.edu/snacks/melting-ice-rising-seas
Hope this helps.
