Understanding Gases and Their Properties

• Gas is a state of matter that is seemingly difficult to comprehend because its physical characteristics are not readily seen.
• Gas behavior is predictable when temperature and pressure are varied.

General Properties of Gas

• Gas has no definite shape or volume.
• Gas volume is based on the volume of its container.
• Gases occupy all spaces available in their container.
• Gases are compressible when pressure is applied.
• Gases also exert pressure.
• Gases expand when heated, and contract when cooled.
• The intermolecular force of attraction between gas particles is negligible.
• Gas particles diffuse easily.

Measurable Properties of Gas

• Volume is equal to the volume of its container, as it occupies all available space.
• Common units of volume used in gas measurements:
  • Liter (L)
  • Milliliter (mL)
  • Cubic meter (m³)
  • Cubic centimeter (cm³)
• Pressure is the force exerted by gas molecules on the walls of its container, divided by the surface area of the container.
• Earth's atmosphere exerts a pressure of 1.013 x 10⁵ N/m² or 1 atm.
• Atmospheric pressure decreases as altitude increases.
• Common units of pressure and their equivalent:
  • 1 atm = 1.013 x 10⁵ N/m² = 1.013 x 10⁵ Pa
  • 1 atm = 760 torr = 760 mmHg
  • 1 atm = 14.696 psi
• Temperature is the average kinetic energy of the particles of gas.
  • Usually determined using a thermometer.
  • Expressed in degree Celsius (°C), degree Fahrenheit (°F), and Kelvin (K).
  • Only Kelvin is used in computations involving temperature of gas.
• Useful formulas for converting units of temperature:
  • °C = (°F - 32) / 1.8
  • °F = 1.8°C + 32
  • K = °C + 273

Standard Conditions of a Gas

• Also known as STP, or Standard Temperature and Pressure.
• Standard temperature is the melting point of ice, at 0°C or 273K.
• Standard pressure is the average atmospheric pressure at sea level, equal to 1 atm.
• One mole of gas occupies a volume of 22.4 L.
• The inverse relationship exists in an enclosed container between the volume and the pressure of a gas.
  • Pushing the plunger increases pressure and decreases gas volume inside the balloon.
  • Pulling the plunger decreases pressure, increasing gas volume.

Boyle's Law

• Formulated by Robert Boyle.
• States that “The volume of a fixed amount of gas is inversely proportional to its pressure at constant temperature.”
  • If pressure decreases, volume increases, and vice versa.

Basic Equation

• P₁V₁ = P₂V₂
  • P₁ = initial pressure
  • V₁ = initial volume
  • P₂ = final pressure
  • V₂ = final volume
• Formulas:
  • P₁ = (P₂V₂) / V₁
  • P₂ = (P₁V₁) / V₂
  • V₁ = (P₂V₂) / P₁
  • V₂ = (P₁V₁) / P₂