Examples why does water expand when heated

The atoms themselves do not expand, but the volume they take up does. When a solid is heated, its atoms vibrate faster about their fixed points. When ice becomes liquid water, it no longer has fixed linear dimensions, but it has volume.

Scientists use a different thermal coefficient -- the coefficient of volume expansion -- to measure the response of liquid water to temperature. This coefficient, which measures fractional changes in volume per degree Kelvin, is not fixed. It increases with mounting temperature until the water starts boiling. In other words, liquid water expands at an increasing rate as the temperature goes up. If the pressure P and number of moles of vapor n maintain at a constant, the volume of steam V increases linearly with temperature T.

In this equation R is a constant called the ideal gas constant. At its melting point, water exhibits a characteristic shared by no other compound. Instead of continuing to expand in the liquid state, it contracts, and its density increases until it achieves a maximum at 40 F 4 C. Incidentally, increasing salinity increases the boiling point and decreases the freezing point. Increasing salinity also lowers the temperature of maximum density.

This effect also helps explain why you are supposed to add salt to ice when making ice cream or to add salt to water when cooking spaghetti although, in this case, the effect on boiling point is minor and the added salt is mainly for flavor. When water freezes, however, bonds are formed that lock the molecules in place in a regular hexagonal pattern.

For nearly every known chemical compound, the molecules are held closer together bonded in the solid state e. Water, however, is unique in that it bonds in such a way that the molecules are held farther apart in the solid form ice than in the liquid.

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