Surface Tension

Surface tension

Surface tension is a measure of the strength of the water's surface film. The attraction between the water molecules creates a strong film, which among other common liquids is only surpassed by that of mercury.

This surface tension permits water to hold up substances heavier and denser than itself. A steel needle carefully placed on the surface of a glass of water will float. Some aquatic insects such as the water strider rely on surface tension to walk on water.

Surface tension is essential for the transfer of energy from wind to water to create waves. Waves are necessary for rapid oxygen diffusion in lakes and seas.

Water – the universal solvent

An extraordinary property of water is its ability to dissolve other substances. There is hardly a substance known which has not been identified in solution in the earth's waters. Were it not for the solvent property of water, life could not exist because water transfers nutrients vital to life in animals and plants.

A drop of rain water falling through the air dissolves atmospheric gases. When rain reaches the earth, it affects the quality of the land, lakes and rivers.

Capillary Action

Water molecules as well as binding to each other, bind to many other substances such as glass, cotton, plant tissues, and soils. This is called adhesion. For example, in a thin glass tube, when the molecules at the edge reach for and adhere to the molecules of glass just above them, they at the same time tow other water molecules along with them. The water surface, in turn, pulls the entire body of water to a new level until the downward force of gravity is too great to be overcome. This process is called capillary action.

Thus water readily wets many materials. Capillary action allows a paper towel or a sponge to be used to soak up spilled water. Without this property, the nutrients needed by plants and trees would remain in the soil. Water's Specific Heat Water has a high heat capacity. Specific heat a measure of heat capacity, is the heat required to raise the temperature of 1 gram of water 1°C. Water, with its high heat capacity, therefore, changes temperature more slowly than other compounds that gain or lose energy.

The heat capacity of water stems directly from its hydrogen bonded structure. Although hydrogen bonds are weak, their combined effect is enormous. As heat is added to ice or liquid water, the energy first breaks hydrogen bonds, which allows the molecules to move freely. Since temperature is a measure of the average kinetic energy of molecules (the rate at which they move), the temperature of water rises slowly with the addition of heat. When the temperature of water drops slightly, many additional hydrogen bonds form and release a considerable amount of energy in the form of heat.

Latent Heat

To make water evaporate, you put energy into it. The individual molecules in the water absorb that energy, and get so energetic that they break the hydrogen bonds connecting them to other water molecules. They become molecules of water vapor. Evaporation is the change of state from liquid to vapor. In the process of evaporation, the molecule absorbs energy. This energy is latent heat. Latent means hidden, so latent heat is "hidden" in the water molecule--we can't feel it, but it is there. Wherever that individual molecule of water vapor goes, it takes that latent heat with it. To get the molecule of water vapor to become liquid again, we have to take the energy away, that is, we have to cool it down so that it condenses (condensation is the change from the vapor state to the liquid state). When water condenses, it releases latent heat.