Question about ice and water?

May 2021 8 1 Report

Question about ice and water?

I start with two glasses of water, both the same volume, same temperature. In one glass, I put an ice cube that is close to melting point. In the second glass, I put an ice cube that is very much colder than melting point. Which cube will cool the water faster?

Update:

The reason I ask the question is.. my understanding is that the melting process absorbs heat, and that's the main way that ice cools your soft drink. So I wondered if *colder* ice would actually cool the soft drink more slowly, since it would take a while before it starts melting. In fact, I figured it would actually freeze some of the water immediately surrounding it, and that would add heat to the liquid. But does anybody actually know for sure?

Update 3:

Juggling Frogs: Thanks for your response. But I wasn't asking which cube would make the water colder. I was asking which would cool the water faster.

Science & Mathematics / Physics

Dr. C

Verified answer

You don't specify, so I'll assume that the cubes are of equal mass and geometry. It certainly is a strange question, as it makes you double-guess the blatantly obvious answer.

Answer: The colder cube will cool the water faster.

Reason: Cooling the water is a heat transfer process. The faster heat can be transfered from the water to the ice, the sooner the water will be cooled. The speed at which this heat flow can occur is proportional to the temperature difference between the water and the surface of the ice.

There are two important factors at work here. For the warm cube, the initial temperature difference between the water and ice will be small. Because the entire cube was initially at the freezing point, the outside of the cube will remain at 0°C while the water becomes cooler, further reducing the difference. For the cold cube, the initial temperature difference will be large. Not only that, but the outside of the cube will remain below freezing as heat is transfered to the center, prolonging the period of larger temperature difference.

There is only 1 caveat to this. Depending on the size and geometry of the glass and the cube, thermal convection of the water could play a substantial role. As the cube melts, it adds cold water to the glass which immediately sinks, displacing warm water which rises to the cube. This added convection brings more water in contact with the cube, than if it simply sat there. However, a cold body in the glass will produce a certain amount of thermal convection anyway. There is a temperature range in which the cold cube might be at a disadvantage, but you specify "very much colder".

Anonymous

The colder cube will cool the glass faster, but not because it is colder. Temperature exchange is limited by the ice cube's surface area and the temperature difference. Both ice cubes will be pretty much 0 degrees C at their surface (although the colder one is colder on the inside), but the warmer cube's surface area will decrease faster as it melts, and it will actually conduct cold slower to the surrounding water as it gets smaller.

Juggling Frogs

This was a good question! My husband thinks it's clear that the colder ice cube would result in a colder glass of ice water.

He suggests considering that it's possible to insert an ice cube so cold that the whole glass of ice water freezes.

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Reply (from my husband): in his extreme case, the surface area of frozen water is growing and will cool the remaining water faster.

badbender001

The cube that is colder because it will absorb more of the energy in the glass then the cube that is near melting.

Linna H

This question depends... If you melted the melted ice cube in a container, that one will cool faster. But on the other hand if it melts in your hand then they will cool about the same time. Try it!

Branshaw

your question is wrong....ice cubes are all the same temperature!!!! they can not be different. they are all at the freezing point of water. thats why the heat of conversion between ice and water is constant....because ice is only one temperature!