3.3 Gas laws

Properties of Gases

  • General Properties:

    • Gases expand indefinitely until they fill the space of their container.

    • Example Gases: Carbon Dioxide (CO₂), Sulfur Dioxide (SO₂).

Expansion

  • Gases expand to occupy the entire volume of the container they are in.

Undefined Shape

  • Gases adapt to the shape of their containers.

  • Compressibility:

    • Gases can be compressed into a smaller volume by applying pressure.

Density and Miscibility

  • Low Density:

    • Gases are less dense than liquids and solids.

  • Miscibility:

    • Two or more gases can mix completely and uniformly.

Pressure in Gases

  • Pressure Definition:

    • Pressure is defined as the force applied to a unit area of surface.

  • Barometer:

    • An instrument used to measure atmospheric pressure.

Atmospheric Pressure

  • Mercury Barometer:

    • Illustration of how a barometer works with mercury to measure pressure.

    • Atmospheric pressure is exerted by the mercury column.

Units of Pressure

  • Atmospheric Pressure Units:

    • 1 atmosphere (atm) = 101.3 kilopascals (kPa) = 760 millimeters of mercury (mm Hg) = 1013 millibars (mbar).

Kinetic Theory of Gases

  • All gases consist of molecules.

  • There are no attractive forces between gas molecules.

  • Gas molecules are in constant rapid motion.

  • The kinetic energy of gas molecules is proportional to the absolute temperature in Kelvin (K).

  • Gases are compressible due to the large spaces between molecules.

Gas Laws

Variables Involved in Gases

  • Key Variables: Pressure, Volume, Temperature, Number of particles

Boyle's Law

  • Formula: P₁V₁ = P₂V₂

    • At constant temperature, the volume (V) of a gas is inversely proportional to its pressure (P).

Charles's Law

  • Formula: V₁/T₁ = V₂/T₂

    • At constant pressure, the volume (V) of a gas is directly proportional to its temperature in Kelvin (K).

Gay-Lussac's Law

  • Formula: P₁/T₁ = P₂/T₂

    • At constant volume, the pressure (P) of a gas is directly proportional to its temperature in Kelvin (K).

Combined Gas Law

  • Formula: P₁V₁/T₁ = P₂V₂/T₂

    • Combines Boyle's, Charles's, and Gay-Lussac's laws.

Ideal Gas Law

  • Formula: PV = nRT

    • P = Pressure, V = Volume, T = Temperature, n = Moles, R = Constant (0.0821 L·atm/mol·K).

Calculating Moles in an Ideal Gas

  • Example Problem:

    • Calculate the number of moles in a 2.44 L gas sample at 25°C and 202 kPa using R = 0.0821 L·atm/mol·K with the formula n = PV/RT.

Class Activities

  • Engage with Gas Laws through various exercises and examples.