Introduction to the Gaseous State

The gaseous state is one of the three fundamental states of matter, alongside solids and liquids. Gases are characterized by their lack of definite shape or volume, as they expand to fill any container they occupy. This is due to the weak intermolecular forces between gas particles, which allow them to move freely and independently.

Key Properties of Gases

  1. Gases conform to their surroundings, taking the shape and size of any container they occupy.


  3. High Kinetic Energy: Gas particles possess high kinetic energy, which enables them to move rapidly and collide frequently with each other and the container walls.

  4. Low Density: Gases have low densities compared to solids and liquids due to the large amount of empty space between their particles.

  5. Compressibility: Gases are highly compressible, meaning their volume can be reduced significantly by increasing pressure.

  6. Diffusion: Gases diffuse readily, mixing with other gases to form homogeneous mixtures.

  7. Effusion: Gases can effuse through small openings, escaping from a container into a region of lower pressure.

  8. Pressure: Gases exert pressure on their surroundings due to the collisions of their particles with the container walls.

Gas Pressure

Pressure is defined as the force exerted per unit area. In gases, pressure is caused by the collisions of gas particles with the walls of their container. The SI unit of pressure is the Pascal (Pa).

Standard atmospheric pressure, or 1 atm, equals 760 mm Hg, 760 torr, or 101325 Pa.


Factors Affecting Gas Pressure

  • Temperature: Increasing the temperature of a gas increases the kinetic energy of its particles, leading to more frequent and forceful collisions with the container walls, resulting in higher pressure.

  • Volume: Decreasing the volume of a gas increases the number of collisions between particles and the container walls, leading to higher pressure.

  • Number of Particles: Increasing the number of gas particles in a container increases the frequency of collisions, resulting in higher pressure.

Gas Laws

  • Boyle's law: Pressure and volume are inversely related at constant temperature. Charles's law: Volume and absolute temperature are directly related at constant pressure.


  • Gay-Lussac's Law: The pressure of a gas is directly proportional to its absolute temperature at constant volume.

  • Combined Gas Law: Combines Boyle's, Charles's, and Gay-Lussac's laws to relate the pressure, volume, and temperature of a gas.

  • Ideal Gas Law: Describes the behavior of ideal gases, which are hypothetical gases that obey the gas laws perfectly.

These gas laws are essential for understanding the properties and behavior of gases in various applications, such as chemistry, physics, and engineering.