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Properties of Water

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  • October 1999
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Properties of Water

Water is essential for life as we know it on earth. It is used by plants and animals for basic biological processes which would be impossible without the use of water. The origin of all life can be traced back to the water in the Earth's precambrien seas. Water is also the universal solvent. It reacts with more elements and compounds than any other substance known to man. Water is a polar molecule made up of on atom of hydrogen and two atoms of oxygen. It is attracted to itself by hydrogen bonds. Hydrogen bonds are weaker than covalent bonds, but collectively these bonds hold water together and give it its cohesiveness. These bonds are also very important to water's ability to absorb heat, as without hydrogen bonds water would have a boiling point of -80 degrees C and a freezing point of -100 degrees C.

In reality, however, water has a boiling point of 100 degrees C and a freezing point of 0 degrees C. The amount of energy needed to raise the temperature of one gram of water by one Celsius degree is called a Calorie. One Calorie is about twice as much energy as you need to warm one gram of most other fluids by the same amount. This makes water much better for regulating the temperatures of animals and the environment.

Water also has a very high heat of vaporization. Converting one gram of cold water into ice requires 80 Calories of energy. Converting the same amount of very hot water into steam requires 540. The high amounts of energy required to change water from its liquid state make water tend to stay a fluid. The process of freezing water involves slowing down the activity of the water molecules until they contract and enter into a solid state. Once the ice is cooled down to 4 degrees or less, the hydrogen bonds no longer contract, but they become rigid and open, and the ice becomes less dense. Because the ice has become less dense, it floats on liquid water. Water freezes from the top down. Once the...