The vapour pressure of a liquid at any temperature is defined as the pressure exerted by the vapour in equilibrium with the liquid at that temperature. T/F
The vapour pressure of a liquid at any temperature is defined as the pressure exerted by the vapour in equilibrium with the liquid at that temperature. T/F
The correct option is A True
Are you wondering about the definition of vapour pressure?
For that, let's first take a look at the process of arriving at the definition and then after that only we will arrive at the definition.
If a liquid is placed in a closed vessel, its molecules may go into the gaseous phase from the liquid phase due to evaporation.
As time passes, more and more molecules leave the liquid and come above the surface of the liquid. The molecules present above the liquid surface are called vapour. These molecules in the vapour phase are also constantly moving, and some of them strike the surface of the liquid, which may be recaptured by the liquid. The process is called condensation.
In the beginning, the rate of evaporation is high. However, as more and more molecules with higher energy leave the liquid, the rate of evaporation decreases with time. On the other hand, as the number of molecules in the vapour phase is very small in the beginning, the rate of condensation is very low. However, with the passage of time, as the number of molecules in the vapour phase increases, the rate of condensation also increases. Ultimately, a stage is reached when the rate of evaporation becomes equal to the rate of condensation, i.e., equal number molecules leave and re-enter the liquid at the same time.
This state is called the state of equilibrium. The pressure exerted by the vapour at this stage (as indicated by a manometer) is called the vapour pressure. It is sometimes called the saturated vapour pressure because the vapour phase is saturated with vapour at this stage.
Hence the vapour pressure of a liquid at any temperature is defined as the pressure exerted by the vapour in equilibrium with the liquid at that temperature.
Are you wondering about the definition of vapour pressure?
For that, let's first take a look at the process of arriving at the definition and then after that only we will arrive at the definition.
If a liquid is placed in a closed vessel, its molecules may go into the gaseous phase from the liquid phase due to evaporation.As time passes, more and more molecules leave the liquid and come above the surface of the liquid. The molecules present above the liquid surface are called vapour. These molecules in the vapour phase are also constantly moving, and some of them strike the surface of the liquid, which may be recaptured by the liquid. The process is called condensation.
In the beginning, the rate of evaporation is high. However, as more and more molecules with higher energy leave the liquid, the rate of evaporation decreases with time. On the other hand, as the number of molecules in the vapour phase is very small in the beginning, the rate of condensation is very low. However, with the passage of time, as the number of molecules in the vapour phase increases, the rate of condensation also increases. Ultimately, a stage is reached when the rate of evaporation becomes equal to the rate of condensation, i.e., equal number molecules leave and re-enter the liquid at the same time.
This state is called the state of equilibrium. The pressure exerted by the vapour at this stage (as indicated by a manometer) is called the vapour pressure. It is sometimes called the saturated vapour pressure because the vapour phase is saturated with vapour at this stage.
Hence the vapour pressure of a liquid at any temperature is defined as the pressure exerted by the vapour in equilibrium with the liquid at that temperature.
