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General Science => General Science => Topic started by: jack_ on 06/03/2019 15:11:56

Title: Can there be gain of enthalpy by freezing water?
Post by: jack_ on 06/03/2019 15:11:56

Hariharan asks:

Can there be gain of enthalpy by freezing water below 0 degree Celsius? If so is the gain of enthalpy by the system or surroundings?

I read that 'thermodynamics teaches that the loss of entropy by freezing the salt solution can be overcome at temperatures below 0 degree Celsius because the gain in enthalpy by freezing water rises when temperature goes down.'

Can you provide any insight?

Title: Re: Can there be gain of enthalpy by freezing water?
Post by: chiralSPO on 06/03/2019 15:30:44

Yes, water releases heat to its surroundings when it freezes--precisely the amount of heat an equal mass of ice extracts from its surroundings to melt (this is called the latent heat of fusion).

The same is true for water turning to steam (highly endothermic) and steam condensing to water (highly exothermic) (this heat is referred to as heat of vaporization).

the equation ΔG = ΔH – TΔS gives the relationship between enthalpy, entropy and temperature (at fixed pressure one must use the equation A = U – TS)

Title: Re: Can there be gain of enthalpy by freezing water?
Post by: Bored chemist on 06/03/2019 19:23:49

If you supercool water then shake it so it freezes, the heat released warms the material to 0C