Gas Equation and Van der Waals Equation

In this article, we will tell you about the ideal gas equation and the Van der Waals equation. Both of these equations are used extensively to study gas molecules. The ideal gas law is used to estimate the volume of gases consumed while the Van der Waals equation is used to correct and predict the lower critical solution behaviour or mixtures including the polymer. Well, there is a lot more to these equations than you think. Keep reading this article to understand more about them.

What is the Ideal Gas Equation?

Before we understand the ideal gas equation it’s important to first know the meaning of the ideal gas equation. So, an ideal gas is a hypothetical gas where the molecules are far apart due to which the intermolecular forces are not considered. In reality, there is no such thing as an ideal gas although it helps in studying how gases respond to changing conditions.

Most of the real gases have the characteristics of the ideal gas. Thus, the ideal gas can be used to study how real gas behaves.

The equation is the combination of Boyle’s law, Charle’s law and Avogadro’s law. Let’s see the meaning of these laws. 

According to Boyle’s law, the volume of a gas at a constant temperature is inversely proportional to the pressure of the system. Charle’s law states that if the pressure is constant then the volume of the gas is directly proportional to its absolute temperature.

Avogadro’s law describes the relationship between the amount of gas and volume.

The ideal gas equation states that when we multiply the pressure and volume of an ideal gas the value that we get is directly proportional to the product of temperature and the number of gas particles. This is the ideal gas equation:

PV=nRT

Where,

P= Pressure

V= Volume

N= Number of moles of the gas

R= The universal gas constant

T= Temperature

Limitations of Ideal Gas Equation:

The main drawback of the ideal gas equation was that it doesn’t work for the low temperature, high density and extremely high pressures. This is because at high pressure we need to take the molecular size and intermolecular forces into consideration. This equation is also not applicable to heavy gases(refrigerants). At the same time, gases that have strong intermolecular forces will also not take into account the ideal gas equation. Due to these limitations, the Van der Waals equation was invented.

Van der Waals Equation:

The Van der Waals equation is a modified version of the ideal gas equation which helps in defining the physical state of the gas. The limitations of the ideal gas law are not present in this modified equation. The Van der Waals equation takes the molecular size and molecular interaction force into consideration. This helps in studying the gas and its properties in great detail. It shows the relationship between the pressure, volume, temperature, and amount of real gases.

The Van der Waals equation is as follows:

(P+an² ⁄ V²) (V-nb)=nRT

P= Pressure

V= Volume

T= Temperature

a= the magnitude of attractive forces between the molecules

b= the volume of the container

Merits of Van der Waals Equation:

• The predictions are much more accurate than the ideal gas equations.
• The equation can also be applied to the fluids.
• The arrangement is in the form of a cubic equation in volume. Due to this cubic equation, we can get three volumes. This will help us to find the volume of the gas at and below the critical temperatures. 
• The constants a and b vary from gas to gas.

Demerits of Van der Waals Equation:

• The equation will only give accurate results only above the critical temperature.
• The equation does not apply to the transition phase of gas to the liquid below a critical temperature.

Conclusion:

As you can see, both the ideal gas equation and the Van der Waals equation are very easy to understand. First, the ideal gas came and was very helpful in the start. But, as more and more research was made on gas molecules the flaws of this equation came into the front. Due to this the Van der Waals equation was invented which helped in studying the molecular size and molecular interaction force in great detail.