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Gas Laws Overview

Jul 8, 2025

Overview

This lecture reviews Boyle's, Charles's, and Gay-Lussac's Laws before introducing the Combined Gas Law for situations involving changes in pressure, volume, and temperature.

Individual Gas Laws

  • Boyle's Law relates pressure and volume; changing one affects the other when temperature is constant.
  • Gay-Lussac's Law relates pressure and temperature; changing temperature affects pressure if volume is constant.
  • Charles's Law relates volume and temperature; changing temperature affects volume if pressure is constant.

Limitations and Need for Combined Gas Law

  • Problems involving changes in more than two variables (pressure, volume, and temperature) cannot be solved with the three individual laws.
  • The Combined Gas Law incorporates all three variables: pressure, volume, and temperature.

Combined Gas Law and Example

  • The Combined Gas Law is: (P₁ × V₁) / T₁ = (P₂ × V₂) / T₂.
  • Used to solve problems where pressure, volume, and temperature all change.
  • Example: A 40.20 L balloon at 1.00 atm and 25.0°C is submerged in water at 11.00 atm and 4.0°C; solving for new volume.
  • All temperatures must be converted to Kelvin: T(K) = T(°C) + 273.
  • Rearranged formula for final volume (V₂): V₂ = (T₂ × P₁ × V₁) / (T₁ × P₂).
  • Plug in values: V₂ = (277 K × 1.00 atm × 40.20 L) / (298 K × 11.00 atm).
  • Simplify units; answer in liters with correct significant figures.

Calculation Steps and Units

  • Temperature conversions: 25.0°C + 273 = 298 K; 4.0°C + 273 = 277 K.
  • Final volume calculation yields 3.38 L (rounded to three significant figures).
  • Kelvins and atmospheres cancel, leaving liters for volume.

Key Terms & Definitions

  • Boyle's Law — At constant temperature, pressure and volume are inversely related.
  • Charles's Law — At constant pressure, volume and temperature are directly related.
  • Gay-Lussac's Law — At constant volume, pressure and temperature are directly related.
  • Combined Gas Law — Relates pressure, volume, and temperature: (P₁ × V₁) / T₁ = (P₂ × V₂) / T₂.
  • Kelvin (K) — SI unit for temperature; required for gas law calculations.

Action Items / Next Steps

  • Practice rearranging the Combined Gas Law to solve for different variables.
  • Convert all temperatures to Kelvin in gas law problems.
  • Watch the recommended video on rearranging gas equations for further clarification.

Full transcript