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Energy of water?

by John Grover
Tags: energy, water
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John Grover
#1
Sep12-13, 08:40 PM
P: 1
Seems to me there are 3 sources of energy released when water freezes:

Release of heat to lower from whatever temp you start with to 0C, latent heat released in the transition to from water at 0 to ice at 0, and the expansion energy released as the water increases in volume during the phase change. I sort of no how to calculate the first two bits, but not sure how to quantify the expansion energy.
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willem2
#2
Sep12-13, 09:08 PM
P: 1,395
The expansion energy depends on the pressure in the medium that surrounds the ice.
It's equal to p ΔV, where p is the pressure and ΔV the change in volume.

In a vacuum it would be 0.

for 1 kg of ice under atmospheric pressure, p is about 10^5 N/m^2 and ΔV is 10^-4 m^3,
so the expansion energy is about 10J.
dauto
#3
Sep13-13, 08:01 AM
Thanks
P: 1,948
The expansion energy is already included in the latent heat which is usually tabulated as latent heat at constant pressure (and so is the specific heat)


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