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Name: Kaylen L.
Status: student
Age: 13
Location: N/A
Country: N/A
Date: 1/13/2003

Why does salt water hold heat better than fresh water?


Here are two of possible ways of interpreting the question and the corresponding answers.

1- For the same volume of water, one fresh, one salted, which one holds more heat? The answer is fresh water. Pure water has the highest specific heat (the amount of heat needed to raise the temperature of 1 kg of a substance by 1 degree C). Addition of salt reduces this heat storing capacity.

2- For the same volume of water, one fresh, one salted, which one boils later (i.e., at a higher temperature), and thus can hold more heat prior to boiling and evaporation? The answer is salt water. Adding salt to water raises its "boiling point", which is the temperature at which it boils. The reason for that is that salt molecules, acting like tiny magnets, tend to hold the water molecules down. Water molecules then need more energy (thus higher water temperature) to be able to escape (evaporate).

Ali Khounsary, Ph.D.
Argonne National Laboratory

There seems to be a myth (I think!) that salt water "holds" heat (whatever that means.) better than fresh water. On either a mass or molar basis the heat capacity of the two are quite similar as is their thermal conductivity. So I ask, "Show me the data that indicates that the two have very different thermal properties."

Vince Calder

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