MCQ Detailed View

The concept of ideal gas behavior comes from the Ideal Gas Law:

$$PV=nRT$$

This law assumes that:

1. 
   

   Gas molecules have negligible volume.

   
   


2. 
   

   There are no intermolecular forces between molecules.

   
   


3. 
   

   Collisions between molecules are perfectly elastic.

   
   

In reality, no gas strictly follows these assumptions. All gases are real gases and deviate from ideal behavior to some extent. The deviations mainly arise because molecules have a finite volume and there are attractive or repulsive forces between them.

To minimize these deviations, conditions must be such that these two effects become insignificant.

• 
  

  At high temperature, the kinetic energy of molecules is very large compared to the weak intermolecular forces. This means the molecules move too fast to be significantly influenced by attractions or repulsions.

  
  


• 
  

  At low pressure, gas molecules are far apart from each other. The intermolecular forces become negligible, and the actual volume occupied by the molecules is very small compared to the total volume of the container.

  
  

Therefore, under high temperature and low pressure, real gases behave almost like ideal gases.

On the other hand:

• 
  

  At low temperature, molecules move slowly, and intermolecular attractions become significant, causing deviation.

  
  


• 
  

  At high pressure, molecules are compressed close together, so their finite volume becomes significant, again causing deviation.

  
  

This principle is particularly important in physical chemistry when studying gas laws, thermodynamics, and real gas equations like the van der Waals equation:

(P+aV2)(V−b)=RT\left( P + \frac{a}{V^2} \right)(V - b) = RT(P+V2a)(V−b)=RT

where a accounts for intermolecular attractions and b accounts for the finite molecular volume.

In summary, real gases show ideal behavior at high temperature and low pressure because both intermolecular forces and molecular size effects are minimized, making them closely follow the ideal gas law.