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Boiling water becomes bigger, but its temperature and pressure do not change
The heat added to the L.H2O between 0 and 100°C can be felt and measured with a thermometer. It is thus called sensible heat (SQ). The Q added to the 100°C water to boil it away is called "latent" because it is stored in the G.H2O and released again when the G.H2O condenses back to L.H2O. LQ is volume Q.
LQ and SQ initially came from the same fire. They differ what the water does with them. Its T rises from 0 to 100°C; its volume increases during the 100°C L.H2O- G.H2O phase transition. Most substances expand as they are heated. The volume of mercury in a thermometer increases slightly as it is warmed. That is why the column lengthens or shortens to show T. Mercury expands when it boils to vapour- as water does. When L.H2O freezes to ice, it becomes bigger and colder at the same time- but its T does not change. The Q removed from L.H2O as it freezes is a sort of negative LQ.
LQ absorption can be used for cooling. This can be observed after swimming on a day when a very hot, dry wind is blowing. One soon becomes so cold that one shivers. The hot dry wind absorbs LQ out of one's body as it dries the water off it. The body, and the hot wind, both have a lower T than before the wind absorbed the moisture and LQ necessary to do this.
This effect is used to measure atmospheric humidity with wet and dry bulb thermometers. The wet bulb is relatively cooler when the air is drier. It is also used to keep water cool in hot, dry climates. The water is put in porous earthenware jars. Water seeping out through the pores sucks heat out of the jars as it evaporates. A sophisticated variant of the same idea is used in absorption chillers. If a warm (e.g. 40°C) dry wind blows over a colder (20°C) sea, both the sea and the wind are T cooled, while the wind absorbs LQ (586 kCal per kg L.H2O evaporated) out of the sea. More LQ is absorbed per kg atmospheric humidity (Φ) evaporating from (20°C) water (586 kCal per kg L.H2O evaporated) than from water boiling at 100°C (539 kCal per kg L.H2O boiled).
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