Question

A graph between U (potential energy) and V (Volume) is plotted at constant temperature for gases A and B.

Correct statement regarding B and A will be respectively

• A. Real gas in which attraction are dominant, ideal gas
• B. Real gas in which repulsions are dominant, ideal gas
• C. Ideal gas, ideal gas
• D. Real gas in which repulsions are dominant, real gas in which attractions are dominant

Answer 1

Answer: (B)

Real gas in which repulsions are dominant, ideal gas

Answer 2

• Analysis of Gas A:

The graph for gas A shows that the potential energy (U) is constant and equal to zero (U=0) regardless of the volume (V). In an ideal gas, there are no intermolecular forces of attraction or repulsion, which means there is no potential energy associated with the interactions between molecules. Thus, U=0 for an ideal gas. Therefore, gas A represents an ideal gas.

• Analysis of Gas B:

The graph for gas B shows that as the volume (V) decreases (moving towards the left on the x-axis), the potential energy (U) increases sharply and is positive. This behavior is characteristic of a real gas at very high pressures or very low volumes. When gas molecules are forced very close to each other, strong repulsive forces between their electron clouds become dominant. Work must be done against these repulsive forces to decrease the volume, which leads to a sharp increase in the system's potential energy. Therefore, gas B represents a real gas in which repulsive forces are dominant.

• Conclusion:

Based on the analysis, gas B is a real gas with dominant repulsive forces, and gas A is an ideal gas. The question asks for the correct statement regarding B and A respectively.

Therefore, B is "Real gas in which repulsions are dominant" and A is "ideal gas".

For an ideal gas, intermolecular forces are assumed to be negligible, so the potential energy (U) is zero and independent of volume (U=0). This matches the curve for gas A. For a real gas, at very small volumes (high pressures), the molecules are very close, and repulsive forces between them become dominant. Work must be done against these repulsions to compress the gas, increasing its potential energy. This is represented by the sharp increase in U as V decreases for gas B.