The Gas Laws Notes

Lesson Overview

  • Discusses various gas laws that relate temperature, pressure, and volume

Focus Question

  • How are a gas's temperature, pressure, and volume related?

New Vocabulary

  • Boyle's Law: Relationship between pressure and volume

  • Absolute Zero: Theoretical lowest temperature

  • Charles's Law: Relationship between temperature and volume

  • Gay-Lussac's Law: Relationship between pressure and temperature

  • Combined Gas Law: Relates pressure, volume, and temperature

Review Vocabulary

  • Scientific Law: A description of a relationship in nature supported by many experiments

Boyle’s Law

  • Definition: States that the volume of a fixed amount of gas at constant temperature varies inversely with the pressure.

  • Mathematical Representation: P1V1 = P2V2

  • Graphical Representation: A graph of volume versus pressure shows a downward curve.

Example Calculation

  • Given: V1 = 10 L, P1 = 1 atm, and P2 = 2 atm

  • Calculate: V2 using Boyle's law.

  • Calculation shows that volume decreases when pressure increases.

  • Real-World Application: A diver's air bubble expands as it rises due to decreased pressure.

Charles’s Law

  • Definition: The volume of a gas is directly proportional to its Kelvin temperature at constant pressure.

  • Key Point: As temperature increases, volume increases.

  • Graphical Note: Zero on the Kelvin scale (0 K) corresponds to zero volume in theory.

  • Absolute Zero: The point where molecular motion theoretically stops.

Example Problem

  • Initial Conditions: A helium balloon occupies 2.32 L at 40.0°C.

  • Final Conditions: What is the new volume at 75.0°C?

  • Conversion Needed: Celsius to Kelvin (T + 273) before calculations.

  • Final Calculation: V2 calculated to be 2.58 L while maintaining constant pressure.

Gay-Lussac’s Law

  • Definition: Pressure of a fixed amount of gas varies directly with the Kelvin temperature when volume is constant.

  • Key Concept: When temperature decreases, pressure also decreases.

Example Problem

  • Initial Conditions: Pressure of oxygen gas in a canister is 5.00 atm at 25.0°C.

  • Final Conditions: What is the new pressure at -10.0°C?

  • Use Kelvin conversion to relate temperature changes to pressure changes.

Combined Gas Law

  • Definition: Describes the relationship among pressure, temperature, and volume for a fixed amount of gas.

  • Formula: P1V1/T1 = P2V2/T2

  • Key Concept: Changes in both pressure and temperature affect volume.

Example Problem

  • Initial Conditions: Gas at 110 kPa and 30.0°C with V1 = 2.00 L.

  • Final Conditions: Pressure increases to 440 kPa and temperature to 80.0°C; determine V2.

  • Conclusion: V2 calculated to be 0.58 L, showcasing the impact of increased pressure and temperature.

Review Quiz Questions

  • According to Boyle’s law, when the pressure doubles, the volume:

    • A) It doubles

    • B) It decreases by half (CORRECT)

    • C) It triples

    • D) It stays the same

  • What is absolute zero?

    • A) The possible lowest theoretical temperature (CORRECT)

    • B) Zero on the Celsius scale

    • C) Atoms are in the lowest possible energy state

    • D) It's zero on the Kelvin scale

  • Which law states that volume is directly proportional to temperature?

    • A) Gay-Lussac’s law

    • B) Boyle’s law

    • C) Charles’s law (CORRECT)

    • D) Combined gas law

  • When applying Gay-Lussac’s law, which variables remain constant?

    • A) Amount of gas, pressure

    • B) Amount of gas, volume

    • C) Amount of gas, temperature

    • D) Amount of gas (CORRECT)