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Anne Marie Helmenstine, Ph.D.

Melting Point Versus Freezing Point

By January 14, 2012

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You might be thinking the melting point and freezing point of a substance occur at the same temperature. Sometimes they do, but sometimes they don't. The melting point of a solid is the temperature at which the vapor pressure of the liquid phase and the solid phase are equal and at equilibrium. If you increase the temperature, the solid will melt. If you decrease the temperature of a liquid past the same temperature, it may or may not freeze!

This is supercooling and it occurs with many substances, including water. Unless there is a nucleus for crystallization, you can cool water well below its melting point and it won't turn to ice (freeze). You can demonstrate this effect by cooling very pure water in a freezer in a smooth container to as low as −42 C. Then if you disturb the water (shake it, pour it, or touch it), it will turn to ice as you watch. The freezing point of water and other liquids may be the same temperature as the melting point. It won't be higher, but it could easily be lower.

Boiling Point of Water | How Salt Melts Ice

Comments

January 22, 2012 at 7:04 am
(1) phil mcewan says:

fifty years ago , plus or minus, I was in charge of the test lab for refrigerators and freezers at Westinghouse corp. in Columbus, O.
All rests were recorded using a Potentiometer.

Hoping you know how a Pot. works, we had to have a thermos, [or jug] full of melting Ice with a thermocouple in it. This was done by using ice cubes, and filing the thermos with ice and water, mixing thoroughly.

This gave us a temperature of 32 degrees,— Always, and any change in the thermocouples plus or minus of that would show us the temperature of the appliance being tested on the Potentiometer.

It just has become a worldwide common term “it’s freezing outside” when the actual temp. was 32 degrees, which is not freezing, — it’s MELTING
The water will freeze if the Temps drops even slightly below that .

The ice and water must be pure of course to start with.

Try that experiment, put some ice and water in a jug, stir it good, put in a thermometer and will stay at 32 , “til all ice is MELTED

Thank you

Phil

January 5, 2013 at 7:52 pm
(2) appreciative user says:

Phil, Thanks for taking the time to write up and share that. I don’t usually bother to write comments on the web, but this was a useful addition that got me thinking so I wanted to thank you and encourage people to share what they know, even if it means writing up something on a random page knowing you’ll never know if anyone uses the information.

January 17, 2013 at 7:51 pm
(3) meow says:

thx phil.. im doing a reseach project and that came in REALLY handy. :)

January 28, 2014 at 11:46 am
(4) Ivony Ndapandula Sakaria says:

At what temperature does water starts to melt

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