Properties of Gases & Kinetic Theory of Gases

What are gases made up of?

Gases are made of particles (molecules, atoms or ions) that are in constant random motion (diffusion)

Diffusion

The spreading of a gas to fill its container

Volume is sensitive to changes in….

Temperature and pressure (gases are easily compressed because they are mostly empty space)

Boyle’s Law

At constant temperature the volume of a fixed mass of gas is inversely proportional to its pressure (pressure increases - volume decreases and vice versa)

Charle’s Law

At constant pressure the volume of a fixed mass of gas is directly proportional to its temperature (pressure increases - volume increase and vice versa)

Kelvin number

+273 onto the Celsius number

Use Kelvin not Celsius

Lussac’s Law

In a reaction between gases, the volumes of any gases reacting or produced, are in the ratio of small whole numbers provided the volumes are measured at the same temperature and pressure

Avogadro’s Law

Equal volumes of all gases under the same temperature and pressure contain the same number of particles.

Assumption 1: Kinetic Theory of Gases

Gases are made up of particles that are in continuous rapid, random motion.

Assumption 2: Kinetic Theory of Gases

There are no attractive or repulsive forces between the particles of a gas

Assumption 3: Kinetic Theory of Gases

The average kinetic energy of the particles is proportional to the temperature in Kelvin

Assumption 4: Kinetic Theory of Gases

The gas particles are so small and so widely spread out that their combined size is insignificant compared with the space that they occupy

Assumption 5: Kinetic Theory of Gases

Collisions between particles are perfectly elastic, i.e. there is no overall loss of kinetic energy in these collisions

Limitations

Contrary to assumption 2: There are van der Waals forces/ Dipole-dipole forces

Contrary to assumption 3: It is not valid under high pressure

What is an ideal gas?

One that perfectly obeys all the assumption of the kinetic theory of gases under all conditions of temperature and pressure