When water changes from a liquid to a gas the process is called __________
The process of conversion of a substance from liquid to gaseous state is called evaporation. When water evaporates we obtain the gaseous form of water, commonly known as steam. This conversion process is endothermic, that is it needs an energy input. This supplied energy raises the temperature of water to its boiling point and a part of it is required for phase change (from liquid to gas) and is called latent heat of vaporization. Production of steam has important consequences for human beings, after all it is through conversion of water to steam that we obtain most of our electricity. Whether we think of a coal-fired thermal power plant or a nuclear power plant, in either of them, water is converted to steam which rotates the turbines and generates electricity. The same process was also used in locomotion (coal-fired engines).
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When water changes from liquid to gas at its boiling temperature the process is called vaporization. When this phase change occurs at a temperature below the boiling point it is called evaporation. Molecules of water in a sample do not all have the same kinetic energy - temperature is a measure of the average kinetic energy of molecules. Even at a temperature below the boiling point for water some molecules in the sample will have enough kinetic energy to change to the gas phase. When this occurs the remaining molecules will now have a lower average kinetic energy, which is why evaporation can be used for cooling.