11.0 GAS LAWS

Gases are all around us, and they behave in predictable ways. Unlike solids and liquids, gases are highly compressible and expand to fill any container. The gas laws describe the mathematical relationships between the four key properties of a gas: pressure (P), volume (V), temperature (T), and amount (n, in moles). This chapter focuses on the relationships when the amount of gas is constant: Boyle's Law (P–V), Charles's Law (V–T), the Combined Gas Law, and Graham's Law which relates the rate of diffusion to the mass of gas molecules.

11.1 FUNDAMENTAL CONCEPTS

Before diving into the laws, it's essential to understand the quantities involved and their units.

11.1.1 Pressure (P)

• Definition: Force exerted per unit area by gas molecules colliding with the walls of the container.
• Common units:
  • Pascals (Pa) or kilopascals (kPa): SI unit. 1 kPa = 1000 Pa.
  • Atmospheres (atm): 1 atm = average atmospheric pressure at sea level ≈ 101.3 kPa.
  • Millimeters of mercury (mmHg): 1 atm = 760 mmHg.
  • Bars: 1 bar = 100 kPa (close to 1 atm).

11.1.2 Volume (V)

• Definition: The space occupied by the gas (the volume of its container).
• Common units:
  • Liters (L) or milliliters (mL): Commonly used in lab work. 1 L = 1000 mL.
  • Cubic meters (m³): SI unit. 1