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consists of only 2 molecules of water at the most. When water is heated, the Brownian motion of molecules also increases. This enhanced motion causes the hydrogen bond of normal water to tear apart. 3) Boiling of water Water boils at 100o C and changes to steam by absorbing latent heat of 100 calories per gm. The freezing latent heat is 32 cal. On evaporation, water expands 530 times. It means volume of lcc of water would become 530cc of vapor. Vapor at higher temperature and pressure is called steam. It can store heat energy. At its critical temperature and pressure, water gets directly converted into superheated steam. Here it looses its “inter-phase" state and as such does not require any latent heat for converting it into steam phase. Heat energy stored in steam can be utilized to drive steam engines or turbines. 4) Evaporation of water In open water-storages, water evaporates from its surface in form of vapor. Rate of evaporation depends on surface area, temp.-difference, and wind velocity etc. Water, it is known, is made up of tiny water molecules. A table spoon of water contains about a trillion of them. Addition of heat makes the molecules move faster. They bump into each other with greater force. When sun heats up the oceans surface, fast moving molecules hit each other hard enough to fly into the air. This is called water vapor. The size of water molecule is very small. About 10 millions of them can be lined up in one mm length. Water molecules on or near the surface should have sufficient Kinetic Energy to overcome liquid phase intermolecular forces. The K.E. is proportional to the temperature of the water. When the faster moving molecules escape, the remaining mols will have lower average K.E., and the temperature of water would thus decrease. This phenomenon of evaporative sweat cooling is responsible for cooling of water in earthen pots or cool feeling after sweating. Three key parts in evaporation are Heat, Humidity and Air movement. Stronger the inter-molecular forces keeping the mols together's are
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