The boiling point is the temperature at which a body changes state from liquid to a gas. The boiling point is a characteristic physical property.
Each pure liquid substance vaporizes and becomes gaseous at a specific temperature. This temperature is called the boiling point. It is also at this temperature that a gas becomes liquid. It is then called the condensation point. Thus, for the same substance, the boiling and condensation points are identical. For example, water boils at 100 °C and water vapour condenses at 100 °C.
Depending on the type of substance, the temperature at which boiling takes place varies enormously. For example, at a normal pressure of 101.3 kPa, liquid water evaporates at 100 °C, whereas a temperature of 2 567 °C is required for copper.
The following concept sheet indicates the boiling point of some pure substances, measured at normal pressure, and of certain molecules.
It is important to indicate the pressure at which the boiling point is determined since changes in pressure change the boiling point. Generally, the higher the pressure, the higher the boiling temperature.
Knowledge of the boiling point allows the identification of pure substances, and is useful in various fields. For example, the frying of potatoes must be done in oil and not in water since the latter evaporates before obtaining the temperature necessary for frying, that is 180 °C.
A mixture of different pure substances has a melting point that depends on:
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the substances that make up the mixture;
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the proportions of the substances in the mixture.
Left: Maple water is boiled so that it turns into steam (gaseous state). This increases the concentration of maple sugar and produces syrup.
Right: In the pressure cooker, the pressure is high, which increases the boiling temperature of the water and reduces the cooking time of food.
