States of Matter

SYNOPSIS

• Boyle’s law: At constant temperature, pressure is inversely proportional to volume for a definite amount of ideal gas.
• Charles’ law: At constant pressure, volume is directly proportional to temperature for a definite amount of ideal gas.
• Gay-Lussac’s law: For a given mass and constant volume, pressure is directly proportional to temperature.
• Avogadro’s law: At the same pressure and temperature, equal volumes of ideal gases consist of equal number of moles or molecules.
• Dalton’s law of partial pressure: If two or more non-reacting gases are kept in a container, the total pressure exerted by the gases in the container is the sum of their partial pressures.
• Graham’s law of effusion and diffusion: The rate of effusion or diffusion of a gas is inversely proportional to the square root of molecular mass or density when compared at the same temperature and pressure.
• Kinetic Theory of Gases:
  

1. A molecule is the smallest particle of the gas.
2. Molecules do not settle under the influence of gravity.
3. Molecules move in a straight line until or unless they collide with each other or with the wall of the container.
4. The volume of gas molecules is very small, so it can be neglected in comparison to the volume of the container.
5. Collisions of gas molecules with each other or collisions between gas molecules and the wall of the container are perfectly elastic.
6. Kinetic energy of gas molecules is directly proportional to temperature.
7. There are neither attractive nor repulsive forces present between gas molecules.

• Root mean square speed: It is calculated by first taking squares of individual velocities, taking their mean and then the square root of the mean.
• Average speed: It is calculated by taking the arithmetic mean of the speeds of different molecules of the gas.

• Most probable speed: It is the speed possessed by maximum number of gas molecules at a given temperature.

• Compressibility factor (Z): It is the ratio of observed volume of a gas to the calculated volume under given conditions of temperature and pressure of the gas.

• Critical temperature: The temperature above which a gas cannot be liquefied no matter how much pressure is applied.

• Critical pressure: Pressure exerted by gas at critical temperature.

• Critical volume: Volume attained by gas at critical temperature and pressure.

• Vapour pressure: It is the pressure exerted by a vapour when vapour is in equilibrium with the liquid or solid form or both.

• Boiling point: The temperature at which the vapour pressure of a liquid becomes equal to the atmospheric pressure.

• Freezing point: The temperature at which the vapour pressure of a liquid becomes equal to the vapour pressure of the solid.

• Surface tension: It is the tendency of a fluid surface to occupy the smallest possible area.

• Viscosity: It is the property of liquids which determines their resistance to flow.