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haysoos2 t1_j6vegpc wrote

Reply to comment by sunsetclimb3r in What are the effects of adding rock salt to a cooler full of ice? by Ok_Kareem_7223

Salt doesn't actually make the water colder. It just lowers the temperature at which a phase change happens.

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jwm3 t1_j6w7ood wrote

This does actually make the water actually colder though, it decreases in temperature to that new phase change temperature melting some of the ice in the process.

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haysoos2 t1_j6wv8hd wrote

So you're saying salt has the magical ability to violate conservation of energy?

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jwm3 t1_j6wx714 wrote

No, not at all. See "enthalpy of fusion". Ice melting is endothermic, it has to take in heat from the environment to happen. By forcing it to melt earlier it pulls in heat energy and makes it's surroundings cooler than they were before. However this isn't violating the law.of conservation of energy because the act of freezing the water is exothermic, it gave off heat energy when freezing. It would violate the laws of conservation of energy if it didn't make it colder because then it wouldn't be balanced with the exothermic freezing.

Instant cold packs work on the same principle. Also, this is really easy to verify in your kitchen with some salt, ice, and a thermometer.

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Appaulingly t1_j6y813l wrote

Energy is conserved. The thermal, kinetic energy of the ice and water is transferred to the potential energy in the bonds of the ice (to break them).

The temperature of a system is only ever directly related to the total energy of a system for an ideal gas.

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haysoos2 t1_j6yc1fe wrote

But if the ice and the water are all at 0⁰ C, then they're going to stay at 0⁰ C no matter how much salt you pour in.

The only way the water goes below 0⁰ C is if the ice starts below zero.

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Appaulingly t1_j6ycp2e wrote

This is not true. You can do the kitchen experiment yourself.

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haysoos2 t1_j6ydj06 wrote

Which part isn't true?

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Appaulingly t1_j6ygnxs wrote

When you add salt to ice+water the temperature decreases. Your misconception is that somehow energy is being removed from the system.

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haysoos2 t1_j6ypc3p wrote

I am extraordinarily skeptical that the temperature will actually decrease if all of the components are already at 0 C.

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Appaulingly t1_j6yujev wrote

If you had water that was for example at 105C, you're stating it would stay at 105C as it boils? And that the boiling would not lead to a decrease in the temperature?

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