Behaviour of Perfect Gas and Kinetic Theory — Predicted 2026

AI-Predicted Question Angles for UPSC 2026

Based on trend analysis, current affairs, and recurring themes in Behaviour of Perfect Gas and Kinetic Theory.

Combined Gas Law with tricky unit conversions

high

NEET frequently tests the Ideal Gas Law and its derivatives. A common way to increase difficulty is by providing mixed units (e.g., pressure in kPa, volume in mL, temperature in Celsius) requiring careful conversion to SI units or consistent non-SI units. Students often make mistakes in converting Celsius to Kelvin or volume/pressure units. A question might involve a multi-step process where one property is changed, then another, requiring sequential application of the gas laws.

Comparison of molecular speeds and specific heats for different gases/conditions

high

Questions comparing $v_{rms}$ for two different gases at the same temperature, or the same gas at different temperatures, are very common. Similarly, comparing $C_V, C_P,$ or $gamma$ for monoatomic vs. diatomic gases is a recurring theme. The ability to quickly apply $v_{rms} propto sqrt{T/M}$ and $gamma = 1 + rac{2}{f}$ is crucial. A slightly harder variant might involve a mixture of gases or a gas undergoing dissociation.

Conceptual understanding of real gas deviations and van der Waals equation

medium

While detailed calculations with the van der Waals equation are less common, conceptual questions about why real gases deviate from ideal behavior (finite volume, intermolecular forces) and under what conditions (high P, low T) are quite possible. Understanding the physical significance of the 'a' and 'b' constants in the van der Waals equation, without necessarily performing complex calculations, is a likely testable area.

Mean free path dependence on pressure, temperature, and molecular diameter

medium

The mean free path is a distinct concept within KTG that is often tested conceptually. Questions might ask how $lambda$ changes if pressure is doubled, or temperature is halved, or if the gas is replaced by one with larger molecules. Direct proportionality to $T$ and inverse proportionality to $P$ and $d^2$ are key relationships to remember.