Boiling Point  and Condensation

The boiling point of a liquid is the temperature at which the liquid changes to vapour

. The reverse of boiling is condensation . The temperature at which liquid changes to vapour is the same with the temperature at which the vapour changes back to liquid.

When heat is applied to a liquid the temperature increases . As the temperature increases bubbles of vapour appear in the liquid. These process is called boiling.

Effect Of Impurities And Pressures On The Boiling And Freezing Points

1.           EFFECT OF IMPURITIES ON THE BOILING AND FREEZING POINTS

When an impurities such as salts, is added to pure water , the salts lower the melting point of the  ice formed from the diluted water. Also the impurity lower  the freezing point of the pure water.

The freezing point of a mixture of salts and water is lower than  .

The application of this effect is found in using salts to melt the ice formed on the road during cold weather. In cooler climates rivers are covered with ice while sea will not freeze because it contain a salt solution.

Impurities raises the boiling point of a pure liquid.

2.          EFFECT OF  PRESSURES ON THE BOILING AND FREEZING POINTS

Reduction in pressure within a liquid lower the boiling point of the liquid and makes it boil at lower temperature.

This is the reason why Aeroplane are built to retain same pressure at high altitude .The higher an Aeroplane fly, the lower the pressure , but the pressure inside remain the same with what is available on the ground. The lower pressure at high altitude makes the blood tend to boil. This affect human blood and causes pain in the body. This is the same reason why Astronauts need to wear space suits to keep them at the right pressure.

In a gas cooker ,the pressure  makes the foods item in the cooker to boil at higher temperature than the normal boiling point. This increases the chance of the item to be cooked faster .

In general

1. Addition of impurities lowers the melting and freezing point of pure solids and pure liquids respectively.
2. Addition of impurities increases the boiling point of pure liquids.
3. Increase in pressure increases the boiling point of a pure liquid.
4. Decrease in pressure increases the melting point of all solids that can expand on solidifying.
5. Decrease in pressure decreases  the melting point of all solids that contract on solidifying e.g. Paraffin

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