Gases and Their Properties

Gases

• Elements that exist as gases at 25°C and 1 atmosphere are:
  • Hydrogen (H₂)
  • Nitrogen (N₂)
  • Oxygen (O₂)
  • Fluorine (F₂)
  • Chlorine (Cl₂)
  • Helium (He)
  • Neon (Ne)
  • Argon (Ar)
  • Krypton (Kr)
  • Xenon (Xe)
  • Radon (Rn)

Physical Characteristics of Gases

• Gases assume the volume and shape of their containers.
• Gases are the most compressible state of matter.
• Gases will mix evenly and completely when confined to the same container.
• Gases have much lower densities than liquids and solids.

Pressure

• Pressure is defined as force exerted per unit area.
• Units of pressure:
  • SI unit: Pascal (Pa)
  • 1 Pa = 1 N/m²
  • 1 atm = 760 mmHg = 760 torr
  • 1 atm = 101,325 Pa = 101.325 kPa

Gas Laws

• Boyle's Law: The volume of a given amount of gas held at constant temperature varies inversely with applied pressure.
  • Mathematical representation: P₁V₁ = P₂V₂ (T and n are constant)
• Charles's and Gay-Lussac's Law: The volume of a given amount of gas held at constant pressure is directly proportional to the Kelvin temperature.
  • Mathematical representation: V₁/T₁ = V₂/T₂ (P and n are constant)
  • Temperature must be in Kelvin: T(K) = t(°C) + 273.15
• Amonton's Law: The pressure of a given amount of gas held at constant volume is directly proportional to the Kelvin temperature.
  • Mathematical representation: P₁/T₁ = P₂/T₂ (V and n are constant)
• Avogadro's Law: The volume of a given amount of gas held at constant temperature and pressure is directly proportional to the number of moles of the gas.
  • Mathematical representation: V₁/n₁ = V₂/n₂

Ideal Gas Equation

• Combines Boyle's, Charles's, and Avogadro's Laws:
  • PV = nRT
  • R is the ideal gas constant: 0.082057 L atm/(mol K)
  • Standard temperature and pressure (STP) is defined as 0°C (273.15 K) and 1 atm.
  • At STP, 1 mole of an ideal gas occupies 22.414 L.

Gas Density Calculations

• Density (d) of a gas is calculated using:
  • d = (PM) / (RT)
  • Molar mass (M) can be calculated from: M = (dRT) / P

Dalton's Law of Partial Pressures

• The total pressure of a mixture of gases is the sum of the partial pressures of each individual gas.
  • Ptotal = P₁ + P₂
  • V and T of the gases must be constant.