Introduction to Kinetic Theory of Gases

The Kinetic Theory of Gases explains the macroscopic properties of gases using the microscopic behavior of molecules. It connects temperature, pressure, and volume of a gas with the motion and energy of its molecules.

This chapter is essential for NEET Physics aspirants as it forms the basis for ideal gas laws, molecular kinetic energy, and speed distributions.

StudentBro notes provide exam-focused explanations and derivations to help NEET students solve conceptual and numerical questions confidently.

Direct Links to Download 2025-26 Physics Notes (PDF)

► Click “Download Here” next to your subject to access the free PDF.

Assumptions of Kinetic Theory

• Gas consists of a large number of identical molecules in random motion.

• Molecules occupy negligible volume compared to the volume of the container.

• No intermolecular forces except during collisions.

• Collisions between molecules and with walls are perfectly elastic.

• Average kinetic energy of molecules is directly proportional to the temperature of the gas.

NEET questions often test these assumptions conceptually or in derivations of gas equations.

Pressure of a Gas

• Gas molecules collide with walls of the container, producing pressure.

• Formula derived from kinetic theory: P = (1/3) (N/V) m v²_rms

  • N = number of molecules

  • V = volume

  • m = mass of a molecule

  • v_rms = root mean square speed

• NEET problems include calculating pressure from molecular motion or vice versa.

Root Mean Square (RMS), Average and Most Probable Speeds

• Root mean square speed (v_rms): v_rms = √(3 k T / m)

• Average speed (v_avg): v_avg = √(8 k T / π m)

• Most probable speed (v_mp): v_mp = √(2 k T / m)

• k = Boltzmann constant, T = absolute temperature, m = molecular mass

• NEET questions often involve comparing these speeds or calculating values for a given gas.

Kinetic Energy of Gas Molecules

• Average kinetic energy per molecule: KE_avg = (3/2) k T

• Average kinetic energy per mole: KE_avg = (3/2) R T

• Relation with temperature: Temperature is a measure of molecular kinetic energy

• NEET numericals include energy calculations and temperature-dependent molecular motion.

Equation of State of an Ideal Gas

• Derived from kinetic theory: PV = (1/3) N m v²_avg

• Ideal gas equation: PV = nRT

• Explains behavior of ideal gases and connects pressure, volume, and temperature.

• NEET problems often involve deriving pressure or volume changes using kinetic theory.

Law of Equipartition of Energy

• Definition: Energy is equally distributed among all degrees of freedom of a molecule.

• For monatomic gases: 3 translational degrees → E = (3/2) RT per mole

• For diatomic gases: 5 degrees at moderate temperature → E = (5/2) RT per mole

• NEET questions may involve molecular energy and heat capacity calculations.

Deviation from Ideal Gas Behavior

• Real gases deviate from ideal behavior at high pressure or low temperature.

• Van der Waals equation explains deviations:

  • [P + a(n/V)²][V − nb] = nRT

• Important for conceptual NEET questions on real vs ideal gas behavior.

Maxwell-Boltzmann Distribution

• Describes distribution of molecular speeds in a gas.

• Most molecules have speeds around v_mp, fewer have very high or low speeds.

• NEET questions often include graphical interpretation or calculation of fractions of molecules in a speed range.

Applications for NEET

• Derivation and understanding of ideal gas law

• Calculating pressure from molecular motion

• Determining rms, average, and most probable speeds

• Solving kinetic energy and temperature-related problems

• Understanding heat capacities using equipartition theorem

StudentBro notes provide clear stepwise explanations and examples for all applications.

Tips for NEET Preparation on Kinetic Theory

1. Memorize key formulas for pressure, kinetic energy, and molecular speeds.

2. Practice RMS, average, and most probable speed calculations.

3. Understand the assumptions of kinetic theory for conceptual questions.

4. Solve energy and ideal gas law numericals using stepwise derivations.

5. Visualize Maxwell-Boltzmann distribution and equipartition theorem for better retention.

Advantages of StudentBro NEET Physics Notes

• Covers pressure, kinetic energy, molecular speeds, ideal gas equation, and Maxwell-Boltzmann distribution

• Step-by-step examples, solved numericals, and diagrams included

• Structured for easy revision and conceptual clarity

• Focused on NEET syllabus and high-yield problems

These notes ensure aspirants can confidently tackle kinetic theory questions in NEET exams.

Conclusion

The chapter Kinetic Theory of Gases is essential in NEET Physics under thermodynamics and gas behavior. Mastery of molecular speeds, pressure, kinetic energy, and Maxwell-Boltzmann distribution is crucial for solving both conceptual and numerical problems.

StudentBro NEET Physics notes provide structured, clear, and exam-focused guidance, enabling aspirants to confidently solve kinetic theory questions and excel in NEET exams.