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States of Matter

Gas laws, kinetic theory, real gases, liquids

Key Concepts
  • Ideal gas: molecules have no volume or interactions; obeys PV = nRT
  • Real gases deviate at high pressure and low temperature
  • Kinetic theory: temperature is proportional to mean kinetic energy
  • Critical temperature T_c: above this, gas cannot be liquefied by pressure alone
  • Intermolecular forces: London < dipole–dipole < hydrogen bond (increasing strength)
Important Formulae
Ideal gas law PV = nRT (R = 8.314 J/mol·K)
Van der Waals equation (P + an²/V²)(V − nb) = nRT
Average kinetic energy KE_avg = 3/2 · kT
Boyle's law PV = constant (T, n fixed)
Charles's law V/T = constant (P, n fixed)
Graham's law of diffusion r₁/r₂ = √(M₂/M₁)
Quick Tips
  • Van der Waals constant a: accounts for intermolecular attraction; b: accounts for finite molecular volume.
  • At STP (0°C, 1 atm): V_molar = 22.4 L/mol; at SATP (25°C, 1 bar): V_molar = 24.8 L/mol.
  • Lighter gases diffuse faster (Graham's law) — H₂ diffuses fastest.
Sample Practice Questions

  1. Ideal gas equation is:

    • PV = RT
    • PV = nRT
    • PV = nRt
    • P = nRT/V²
    Show answer

    Answer: PV = nRT

  2. Avogadro's law: equal volumes of all gases at same T and P contain:

    • Equal mass
    • Equal number of molecules
    • Equal kinetic energy
    • Equal moles of atoms
    Show answer

    Answer: Equal number of molecules

  3. Critical temperature is the temperature above which:

    • Gas expands infinitely
    • Gas cannot be liquefied by pressure alone
    • Liquid vaporises spontaneously
    • Solid melts directly
    Show answer

    Answer: Gas cannot be liquefied by pressure alone

  4. Charle's law: at constant pressure, V ∝ :

    • 1/T
    • T²
    • T (absolute temperature)
    • √T
    Show answer

    Answer: T (absolute temperature)

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Practice Questions

Practice 20 randomly selected NEET questions on States of Matter. Answers are revealed after each question.

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