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Core Gas Laws Overview

Jul 8, 2025

Overview

This lecture covers the core gas laws describing the relationships between pressure, volume, and temperature, along with unit conversions and example problems.

Pressure Units & Conversions

  • Common pressure units: atmosphere (atm), millimeters of mercury (mmHg), torr (Torr), and pounds per square inch (psi).
  • 1 atm = 760 mmHg = 760 Torr = 14.69 psi.
  • Pressure conversions may require dimensional analysis (unit cancellation in stepwise multiplication).
  • Always ensure pressure units match in calculations.

Boyle's Law (Pressure-Volume Relationship)

  • Boyle's Law: For a fixed amount of gas at constant temperature, pressure and volume are inversely related (P₁V₁ = P₂V₂).
  • If pressure increases, volume decreases, and vice versa.
  • When solving, match initial and final pressure and volume units.

Charles's Law (Volume-Temperature Relationship)

  • Charles's Law: At constant pressure, gas volume is directly proportional to its temperature in Kelvin (V₁/T₁ = V₂/T₂).
  • Convert all temperatures to Kelvin before using the law.
  • Volume and temperature increase or decrease together.

Gay-Lussac's Law (Pressure-Temperature Relationship)

  • Gay-Lussac’s Law: At constant volume, pressure is directly proportional to temperature in Kelvin (P₁/T₁ = P₂/T₂).
  • Both pressure and temperature must be in compatible units (pressure units match, temperature in Kelvin).

Combined Gas Law

  • Combined Gas Law: Relates pressure, volume, and temperature (P₁V₁/T₁ = P₂V₂/T₂).
  • Use when five out of six variables (P₁, V₁, T₁, P₂, V₂, T₂) are given.
  • Ensures all units for each property (pressure, volume, temperature) match between initial and final states.

Key Terms & Definitions

  • Atmosphere (atm) — A standard unit of pressure, equal to 760 mmHg and 14.69 psi.
  • Millimeter of Mercury (mmHg) — Unit of pressure based on the height of a mercury column.
  • Torr — Unit of pressure equivalent to 1 mmHg.
  • Pounds per square inch (psi) — Imperial unit for pressure.
  • Kelvin (K) — Absolute temperature scale used in gas law calculations.
  • Boyle’s Law — P₁V₁ = P₂V₂ (inverse P-V relation).
  • Charles’s Law — V₁/T₁ = V₂/T₂ (direct V-T relation).
  • Gay-Lussac’s Law — P₁/T₁ = P₂/T₂ (direct P-T relation).
  • Combined Gas Law — P₁V₁/T₁ = P₂V₂/T₂ (relates P, V, T).

Action Items / Next Steps

  • Memorize the pressure unit conversions and the combined gas law equation.
  • Practice converting between pressure, volume, and temperature units.
  • Complete any assigned homework problems involving gas law calculations.

Full transcript