Physico-chemical feature of pure water

Physico-chemical feature of pure water

Heat of Vaporization

Water vaporizes very slowly when heated, i.e. water has a very high latent heat of vaporization (evaporation). Vaporization is a process in which thermal energy is supplied to overcome the attractive forces between water molecules (mainly hydrogen bonds in liquid water).

Depending upon temperature, the amount of heat required for the vaporization of 1g of water ranges from about 500 to 600cd.   

Limnological Significance

If the heat of vaporization is low then natural water bodies could have dried up very quickly but as it is very high the water bodies vaporize very slowly and most of them do not dry up.

Specific Heat

The heat of a substance refers to its capacity to absorb thermal energy in relation to temperature change at constant volume. Water holds a great amount of heat with a relatively small change in temperature. The unit of measure of specific heat is the gram calorie which is defined as the amount of heat required to raise the temperature of 1g of water from 14.5C to 15.5C. Water is the basis of this parameter and is said to have a specific heat of 1.

Limnological Significance

It acts as a buffer against wide fluctuations in temperatures, thereby making better terrestrial climates near large bodies of water. An aquatic organism is subjected to much narrower ranges of temperatures than a land form. Whereas land areas may reach 38C or more, lakes seldom exceed 27C. The slow rate of seasonal cooling and warming of lakes and streams in due the high specific heat of water. For the some reason, changes in lake temperatures lag behind atmospheric fluctuations. In thermal waters, dissolved substances lower the specific heat.

Latent Heat of Fusion

The heat taken up in the change of water from a solid state to liquid phase with no change in temperature is termed the latent heat of fusion. Specifically, 79.7cal of heat are required to melt 1g of ice at 0C.

Limnological Significance

In cold regions of the earth melting of ice and formation of ice occur slowly as latent heat of fusion is about 80cal for which change of aquatic environment does not take place rapidly and as a result aquatic organisms do not face serious situations.