Properties and Laws of Gases

Study Notes

Temperature: Use Kelvin in calculations. Convert Celsius to Kelvin by adding 273. A 10°C change is the same as a 10K change.
Pressure: Use Pascals (Pa) in calculations. Convert kPa to Pa by multiplying by 1000.
Volume: Use cubic meters (m³) in calculations. Convert cm³ to m³ by multiplying by 10⁻⁶.
Standard Temperature and Pressure (STP): Standard temperature is 273 K. Standard pressure is 1 x 10⁵ Pa (100 kPa).
Volume Variation: Gas volume changes with temperature and pressure. To compare gas volumes, temperature and pressure must be constant.

Boyle's Law: For a fixed mass of gas at constant temperature, pressure multiplied by the inverse of volume (P × 1/V) is constant.
Charles' Law: For a fixed mass of gas at constant pressure, volume is directly proportional to temperature (in Kelvin). (V ∝ T). Consistent with the ideal gas law (PV=nRT).
Avogadro's Law: Under the same conditions of temperature and pressure, equal volumes of gases contain the same number of molecules/atoms.
Gay-Lussac's Law: The volumes of reacting gases and their gaseous products are in small whole number ratios when measured at the same temperature and pressure.

Molar volume: The volume occupied by one mole of any gas.
Standard Temperature and Pressure (STP) and Room Temperature and Pressure (RTP): Common units used.

Assumptions:
- No attractive or repulsive forces between gas molecules.
- Gas molecules are small and widely separated.
- Collisions are perfectly elastic (no energy loss).
Ideal Gas: A gas that perfectly follows the assumptions of the kinetic theory under all conditions of temperature and pressure.

Forces of attraction: Forces of attraction (e.g., Van Der Waals forces) between molecules become important under high pressures or low temperatures.
Volume: The volume occupied by the gas molecules themselves is not negligible at high pressures.