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States of Matter: Gases Β· Interactive Lecture

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Class XI Β· Chemistry Β· Unit 4 Β· Interactive Lecture

States of Matter: Gases

The complete lecture β€” gases come alive in the live panel as you read. Scroll down; the animation keeps pace, and you can drive the gas simulator yourself.

1 β€” The gaseous state

Gas particles are far apart and move freely, so a gas has no fixed shape or volume, is highly compressible, has low density, and exerts pressure in all directions.

A gas's state is fixed by P, V, T and n.
2 β€” Pressure of a gas
  • Pressure β€” force per unit area from molecules hitting the walls.
Units1 atm = 760 mmHg = 101325 Pa = 1.013 bar
3 β€” Boyle's law
Boyle's law (constant T)V ∝ 1/P Β· PV = constant Β· P₁V₁ = Pβ‚‚Vβ‚‚
worked
2 dmΒ³ at 1 atm β†’ at 4 atm: (1)(2)=(4)V β†’ 0.5 dmΒ³
4 β€” Charles's law
Charles's law (constant P)V ∝ T Β· V/T = constant Β· V₁/T₁ = Vβ‚‚/Tβ‚‚ (T in K)
Absolute zero = βˆ’273 Β°C = 0 K. Always use kelvin.
5 β€” Gay-Lussac's & Avogadro's laws
  • Gay-Lussac β€” constant V: P ∝ T.
  • Avogadro β€” constant T,P: V ∝ n; 1 mole gas = 22.4 dmΒ³ at STP.
6 β€” The ideal-gas equation
Ideal gas equationPV = nRT · R = 0.0821 dm³·atm·K⁻¹·mol⁻¹

All the gas laws combine here. Move the sliders in the live panel: shrink the box (lower V) or heat it (higher T) and watch the pressure climb.

7 β€” Dalton's law of partial pressures
Dalton's lawP_total = P₁ + Pβ‚‚ + … Β· Pα΅’ = xα΅’ Β· P_total
8 β€” Graham's law of diffusion
Graham's lawrate ∝ 1/√M Β· r₁/rβ‚‚ = √(Mβ‚‚/M₁)
9 β€” Kinetic Molecular Theory
  • Random, continuous, straight-line motion.
  • Negligible molecular volume; no intermolecular forces.
  • Elastic collisions; average K.E. ∝ absolute temperature.
10 β€” Temperature & molecular speed
RMS speedc_rms = √(3RT / M)
11 β€” Real gases
van der Waals(P + anΒ²/VΒ²)(V βˆ’ nb) = nRT
12 β€” Liquefaction of gases
  • Critical temperature β€” above it a gas can't be liquefied by pressure alone.
13 β€” Worked numericals
combined
2 dmΒ³, 1 atm, 273 K β†’ 2 atm, 546 K: Vβ‚‚ = 2 Γ— Β½ Γ— 2 = 2 dmΒ³
partial pressure
2 mol Nβ‚‚ + 3 mol Oβ‚‚, total 5 atm β†’ P_Oβ‚‚ = (3/5)(5) = 3 atm
14 β€” Exam recap
  1. Gas properties; pressure & units; STP.
  2. Boyle, Charles, Gay-Lussac, Avogadro.
  3. PV = nRT & the combined gas law.
  4. Dalton's & Graham's laws.
  5. KMT postulates; K.E. ∝ T.
  6. Real gases & van der Waals.
Next: πŸ“ Practice Β· πŸ§ͺ Virtual lab
βš› Live panelGases
Scroll the lecture β€” this panel animates each concept as you reach it.