If an evacuated container is partially filled with a liquid, a portion of liquid evaporates to fill the remaining volume of the container with vapour. Initially the liquid evaporates and vapour.
Initially the liquid evaporates and pressure exerted by vapours on the walls of the container (vapour pressure) increases.
After some time it becames constant, an equilibrium is estay between luquid phase and vapour phase
Vapour pressure at this stay is known as equilibrium vapour pressure or saturated vapour pressure.
Since process of vapourisation is temperature dependent; the temperature 🌡️ must be mentioned while reporting the vapour pressure of a liquid.
When a liquid is heated in an open vessel pressure of a liquid vapourises from the surface. At the temputure at which vapour pressure vapourisation throughout the bulk of y liquid and vapour expand freely into the surroundings.
The temperature at which vapour Pressure of liquid is equal to the external pressure is called boiling temperature at the pressure. Vapour pressure of some common liquids at various temperatures .
At 1 atm pressure boiling temperature is called normal boiling point. If pressure is 1 bar then the boiling point is called Standard boiling point of the liquid.
Standard boiling point of the liquid is slightly lower than the normal boiling point because 1 bar pressure is slightly less than 1 atm pressure. The normal boiling point of water is 99.6°C (372.6K).
At high altitudes atmospheric pressure is low. Therefore liquid at high altitudes boll at lower temperatures in comparison to that at sea level. Since water 💧 boils at low temperatures on hills, the pressure cooker is used for cooking food. In hospitals surgical instruments are sterilized in autoclaves in which boiling point of water is increased by increasing the pressure above the atmospheric pressure by using a weight covering the vent.
Boiling does not occur when liquid is heated in a closed vessel. On heating continuously vapour pressure increases. At first a clear boundary is visible between luquid and vapour phase because luquid is more dense than vapour. As the temperature increases more and molecules go to vapures phase and density of vapour rises.
At the same time luquid becames less dense. It expands because molecules move apart.
When density of luquid and vapour becames the same; the cley boundary between luquid and vapours disappears. This temputure luquid and vapours disappears. This temputure is called critical temperature.
