How much heat must be removed from 0.45 kg of water at 0 ∘C to make ice cubes at 0 ∘C?
As you know, water changes to ice at a constant temperature....that is, you must remove 'heat' from the water to make if form ice, but the temperature will not change.
At STP (Standard Temperature and Pressure) this occurs at 0 degrees C (or 32 Degrees F)......the amount of heat to be removed for this to happen is the 'Latent heat' of the substance....each substance has its own latent heat value ...... molten lead will form a solid at a significantly higher temperature and with a different latent heat value.
For WATER the latent heat of FUSION (going from a solid crystal to liquid or vica versa) is 334 kj/kg (I had to look that one up...it has been many years since I learned that)
so for .45kg of water to FREEZE It starts at 0 degrees and when it turns to ice it is still at 0 degrees
.45kg (334 kj/kg) = 150.3 kj or 150300 joules of energy must be removed to make the ice.
If you want to make it back into wate you will have to ADD 150300 j of heat energy to it ! Cool?
~jc
