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# The normal boiling point of a liquid is defined as

### Question

The normal boiling point of a liquid is defined as

### Options

A) the temperature at which its vapour pressure equals the atmospheric pressure

B) the temperature at which bubbles begin to form

C) the temperature at which the vapour pressure equals 1 temperature

D) the temperature at which the rate of condensation of vapour equals the rate of vaporisation of the liquid

E) the temperature at which the space above the liquid is saturated

### Explanation:

*The boiling point of a liquid is the temperature at which its saturated vapour pressure equates the pressure of the external air around it.
*The normal boiling point of a liquid is the temperature at which its vapour pressure is equal to 1 atm.
Here are some differences between boiling point and normal boiling point:
*Sometimes, the pressure of the air surrounding the liquid being heated can be greater or less (eg the pressure in a vacuum is less than the atmospheric pressure) than the atmospheric pressure, so the temperature at which the vapour pressure of the liquid equals the pressure of the air around it is the BOILING POINT.
*But if the liquid is being heated under normal atmospheric pressure, then the temperature at which the vapour pressure of the liquid equals the atmospheric pressure (which was defined by IUPAC to be 1 atm or 760 torr, 760 mmHg, 101325 pascal, 101325 N/m2) is the NORMAL BOILING POINT of the liquid.

## Dicussion (1)

• *The boiling point of a liquid is the temperature at which its saturated vapour pressure equates the pressure of the external air around it.
*The normal boiling point of a liquid is the temperature at which its vapour pressure is equal to 1 atm.
Here are some differences between boiling point and normal boiling point:
*Sometimes, the pressure of the air surrounding the liquid being heated can be greater or less (eg the pressure in a vacuum is less than the atmospheric pressure) than the atmospheric pressure, so the temperature at which the vapour pressure of the liquid equals the pressure of the air around it is the BOILING POINT.
*But if the liquid is being heated under normal atmospheric pressure, then the temperature at which the vapour pressure of the liquid equals the atmospheric pressure (which was defined by IUPAC to be 1 atm or 760 torr, 760 mmHg, 101325 pascal, 101325 N/m2) is the NORMAL BOILING POINT of the liquid.