Kinetic Theory of Gases — Syllabus
NIOS · Class 12 · Physics
What Kinetic Theory of Gases covers in NIOS Class 12 Physics: 4 topics, for the 2026-27 session. Part of the NIOS Class 12 Physics syllabus.
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Topics in Kinetic Theory of Gases
Thermal Energy: Heat Capacity and Specific Heat
- Heat and temperature are DIFFERENT concepts: heat is energy transferred due to temperature difference; temperature is a measure of average kinetic energy of molecules.
- Specific heat capacity (C) is the amount of heat required to raise the temperature of 1 kg of a substance by 1°C or 1 K.
- Formula: ΔQ = mCΔθ, where ΔQ = heat supplied (J), m = mass (kg), C = specific heat (J kg⁻¹ K⁻¹), Δθ = temperature rise (K or °C).
Thermal Expansion: Linear, Superficial, and Cubical
- When heat is supplied to a substance, it expands. Expansion can be in length (linear), area (superficial), or volume (cubical).
- All three coefficients are interconnected: β = 2α and γ = 3α
- Linear expansion: Δl = α l₀ Δθ, where α = coefficient of linear expansion (unit: K⁻¹ or °C⁻¹)
Assumptions and Pressure of an Ideal Gas (Kinetic Theory)
- Kinetic Theory connects MACROSCOPIC properties (P, V, T) with MICROSCOPIC properties (mass, speed of molecules).
- An IDEAL GAS is one whose molecules are point masses with no intermolecular forces between them.
- At room temperature and low pressure, real gases behave approximately like ideal gases.
Kinetic Interpretation of Temperature and Mean Kinetic Energy
- Combining PV = (1/3)NmĈ² with ideal gas law PV = nRT gives the kinetic interpretation of temperature.
- Mean kinetic energy per molecule = (1/2)mĈ² = (3/2)kT, where k = Boltzmann constant = 1.38 × 10⁻²³ J K⁻¹
- CRITICAL INSIGHT: Kinetic energy of a molecule depends ONLY on absolute temperature T, NOT on its mass. At the same temperature, all gas molecules (heavy or light) have the SAME average kinetic energy
Key Concepts
Central concept: Kinetic Theory of Gases
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