Why the liquids that have higher vapour pressure have low boiling point

Liquids with higher vapor pressure have lower boiling points because:

- Increased Kinetic Energy: Higher vapor pressure indicates that more molecules in the liquid have enough kinetic energy to overcome intermolecular forces and escape into the gas phase.

- Lower Intermolecular Forces: Liquids with higher vapor pressure typically have weaker intermolecular forces holding their molecules together. This makes it easier for molecules to break free and vaporize.

- Boiling Point Definition: The boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure. Liquids with higher vapor pressure reach this point at a lower temperature because they have more molecules with sufficient kinetic energy to vaporize.

Relationship between Vapor Pressure and Boiling Point:

The Clausius-Clapeyron equation describes the relationship between vapor pressure (P) and boiling point (Tb):

```
ln(P) = -ΔHvap/(R-Tb) + C
```

- ΔHvap is the enthalpy of vaporization (energy required to vaporize 1 mole of liquid)
- R is the ideal gas constant
- C is a constant

From this equation, we can see that a higher vapor pressure (ln(P)) corresponds to a lower boiling point (Tb).

Examples:

- Ethanol has a higher vapor pressure than water, so it boils at a lower temperature (78.3°C) than water (100°C).
- Diethyl ether has a very high vapor pressure and a low boiling point (-43.5°C).