Why does ice crack in hot water?

Question

When you have a hot beverage, tea for example, and you place an ice cube in it, you hear some cracking noises. Then, you begin to see the cracks in the ice cube. Why is that?

Answer 1

Thermal stress/shock

Certain parts are expanding/contracting fast than others.

Answer 2

Let's assume your freezer is at -18 Celsius. Once an ice cube has been in there for a while, it is also at -18 C.

Now you drop the ice cube into a hot beverage, and the surface of the ice cube is heated up to 0 C as it melts. Meanwhile, however, the interior of the ice cube is still near -18 C.

Most materials expand as they are heated, and in the solid phase, water is no exception. So, you have a solid block of material and the outside is trying to expand while the interior stays put. This relative motion induces stress in the ice (known as thermal stress). Ice isn't particularly strong, and is also very brittle, so the stress quickly overwhelms the material's strength, and the ice breaks.

Answer 3

Unlike most materials, water actually expands slightly when it becomes a solid (ice). Rapid inhomogeneous heating will cause portions of an ice cube to quickly distort and shrink faster than cooler regions. With a large enough temperature gradient this can cause significant fracturing in a short amount of time.

You may also notice that if you cool a glass down in the freezer and then fill it with hot water, the rapid thermal expansion of glass will cause it to violently fracture. I strongly recommend you do not try this on purpose.

Answer 4

as the outside of the ice block heats up quicker than the inner (ice being a notorious weak conductor of heat) its volume expands faster than what the inside, still relatively cold, can keep up with. the only way to meet the smaller volume of the inside with the increased volume of the outer, is to crack and separate the two.