Modelling a gas

Introduction to Modelling a Gas

• Gases are modelled as a large number of tiny particles called molecules.
• These molecules are in constant, random motion, colliding with one another and the walls of their container.
• Despite their number, the total volume of the gas molecules is considered negligible compared to the volume of the container.
• Gas molecules are considered to be perfectly elastic, meaning they lose no kinetic energy during collisions.

Assumptions of the Kinetic Theory of Gases

• Gases are composed of microscopic particles in random motion.
• The gas molecules are considered to be point particles; i.e., they are treated as if they are points in space.
• Collisions between gas molecules, or between a molecule and the container’s wall, are elastic; i.e., there is no net loss or gain in the overall kinetic energy.
• There are no intermolecular forces between gas molecules.
• The individual motion of gas molecules is unaffected by the motion of other molecules unless a collision occurs.
• The average kinetic energy of gas molecules is proportional to the gas’s absolute temperature.

Ideal vs. Real Gases

• Real gases follow the kinetic theory assumptions at high temperatures and low pressures.
• At high pressures and low temperatures, real gases deviate from these assumptions due to the presence of intermolecular forces and the finite size of gas molecules.
• In these conditions, an ideal gas is a theoretical construct where the kinetic theory assumptions always apply. Ideal gases do not exist but this model is useful for understanding gas behaviour.

Gas Laws

• Boyle’s law: At a constant temperature, the volume of a gas is inversely proportional to its pressure.
• Charles’s law: At a constant pressure, the volume of a gas is directly proportional to its temperature in kelvin (absolute temperature).
• Avogadro’s law: At a constant temperature and pressure, the volume of a gas is directly proportional to the number of gas molecules.
• These laws can be combined into the ideal gas equation, PV=nRT, where P is the pressure, V is the volume, n is the number of molecules, R is the gas constant, and T is the temperature.

Gain a deep understanding of these principles, and practice applying these laws to different problems. Remember, every molecule in a gas sample contributes to its pressure, volume, and temperature.