________________
in the liquid state, the more energy that must be put-in order to evaporate them. When the water vapor condenses to liquid or solid phase, it releases its latent heat as sensible heat on to the surface. This is the reason why steam is far more effective in heating than boiling water. Latent heat is also called enthalpy of transformation. Latent heat of fusion = 334 J/g, and Latend heat of vapour = 2262J/g at 100°C Molar heat of vaporization for water is 40.7kJ/mol. As the air rises, it gets colder. These molecules move more slowly and pull closer together. This condenses and forms clouds. When the droplets of water are too heavy to stay in the cloud, they fall down as rain or snow. 5) Freezing of water Water has a density of 1 gm per cc at 20°C. It varies with temperature. It starts freezing at 4° C but exhibits a peculiar behavior between 4°C and 0°C due to change in lattice structure of its molecules. It expands and becomes lighter on freezing at 0°C. That is why, ice floats on water. (Iceberg remains 9/1064 submerged below the water surface). As the water mass cools, it contracts. Its highest density is reached at 3.98° C. Then it starts expanding in volume. Its surface becomes cooler. But due to expansion, it remains lighter and does not move towards bottom. The bottom water remains heavier and hotter than the surface water. As such, water starts freezing at the top. This is a wonderful quality bestowed by the nature, because below the frozen surface, liquid water continues to support aqua-life in the oceans. Had it behaved like other liquids, all the sea creatures would have been frozen and perished in the cold regions. But due to this special property of water, life survives in the Arctic and Antarctic regions also, beneath the frozen ocean surfaces. 6) At Human body Temperature (37.5°C) 1) Specific Heat: Water has very high specific heat. However, at 37.5oC, water has minimum specific heat. At this temperature the specific structure of
Jain Education International
For Private & Personal Use Only
www.jainelibrary.org
