The Relation Between Vapour Pressure And Temperature

Both the vapour pressure and temperature are extremely important to all the life forms on the Earth. You might have a brief idea about them but do you know that both vapour pressure and temperature share an interesting relationship? If your answer is No then you have landed on the right page. In this article, we will tell you about the relationship between vapour pressure and temperature.

Before we tell you about their relationship, it’s extremely important to understand their core meaning and what they actually do. They will help you to better understand how they correlate to each other. So, let’s start first with vapour pressure.

What is Vapour Pressure?

To understand vapour pressure let’s go back to the basics and understand the meaning of evaporation and vapour. In evaporation, the liquid turns into a gas and the tiny water molecules that you can see on the liquid surface are called vapour.

Pressure in simple words means the force that mass exerts over the other object. We all know a lot of things exert pressure but you will be surprised to know that vapour also employs pressure.

So, putting things altogether vapour pressure can be defined as the pressure exerted by the vapour with its condensed phases in the thermodynamic equilibrium in a closed container. 

If we study the equilibrium pressure then we can find the evaporation rate of the liquid. The substance with a high vapour pressure at room temperature is commonly referred to as volatile. When the temperature of a liquid increases the kinetic energy of its molecules also increases. Due to this the molecules which undergo the process of vapour also increase which ultimately increases the vapour pressure.

What is Temperature?

Temperature as you all might know is a measure that helps us understand how hot or cold something is. In more technical terms it measures the average kinetic energy of the particles in an object. An object which has a high amount of kinetic energy will have a high temperature. Solids, liquids and gases all have a certain kind of temperature.

Relation Between Vapour Pressure And Temperature:

Temperature is the only factor that affects vapour pressure. The vapour pressure is directly proportional to temperature. This means that as the temperature of a liquid or solid increases its vapour pressure also increases.  Likewise, if the temperature of the liquid decreases the vapour pressure will also decrease. The vapour pressure is not affected by the amount of liquid available in the containers, be it 2 litres or 30 litres, at the same temperature both the samples will have the same vapour pressure. 

In more technical terms, when the temperature is high the molecules get more energy to escape from the solid or liquid. Conversely, when the temperature is low the molecules are not able to get sufficient energy to escape from the solid or liquid.

Clausius-Clapeyron Equation:

The Clausius-Clapeyron equation describes the phase transition (changes that occur among the basic states of matter i.e solid, liquid and gas) between two phases of matter of a single constituent (one having the same composition).

Thus, this equation can help us in finding the vapour pressure as a function of temperature. Secondly, it can also help in finding the heat of the phase transition that occurs during pressures at two temperatures. Many people think that the graph which represents the relationship between temperature and pressure of a liquid is straight. But, this is not true. Instead, the graph is curved

The vapour pressure in the water tends to increase at a faster rate when compared to the temperature. Here, the Clausius-Clapeyron can be used. Now, the Clausius-Clapeyron equation looks something like this: