__SS 1 CHEMISTRY__

__Lesson 2__

__TOPIC__**: The kinetic theory of gases**

There are two types of gases, namely:

- Ideal gases
- Non-ideal or real gases.

An ideal gas is a gas that obeys the gas laws at all temperature and pressure.

A real gas is a gas do not obey gas laws at all temperature and pressure; the only obey gas laws at high temperature and low pressure.

The summary of the kinetic theory of gases includes the following:

- Every gas consist of a very large number of tiny particles called molecules.
- The molecules of a gas within a container are in a state of constant high speed in all possible directions.
- The pressure of a gas on any surface is the result of continuous collision on the surface by its molecules.
- The molecules of a gas exert no appreciable attraction on each other and behave as perfectly elastic body.
- The absolute temperature of a gas is a measure of the average kinetic energy and is proportional to it.
- There is not effect of gravity on the motion of a gas.
- The actual volume of a gas is negligible compare with the total volume it occupies.

__VARIABLES USED FOR DISCRIBING GAS BEHAVIOURS__

- Volume
- Pressure
- Temperature

__VOLUME__

The volume of a gas is the size of the space it occupies, which is the capacity of it container. The SI unit of volume is the cubic metre (m^{3}). The practical units of volume are the cubic centimetre (cm^{3}), cubic decimetre (dm^{3}) and the litre (L). the cubic centimetre is equivalent to millilitre (ml).

1L = 1dm^{3} = 1000cm^{3} = 1000ml.

__PRESSURE__

Pressure is defined as the total force exerted on a surface per unit area of the surface. The SI unit of pressure is to Pascal (Pa), the pressure produced when a force of one Newton is acting on an area of one square metre.

(i.e. Newton per square metre).

Other units of pressure are atmosphere (atm), millimeter of mercury (mmHg).

1atm =760mmHg

__TEMPERATURE__

Temperature is a measure of how hot a substance is.

The SI unit of temperature is degree centigrade or Celsius (^{o}C). another SI unit of temperature is the Kelvin (K). The starting point of Celsius scale is the freezing point of water at 0^{o}C while the starting point of Kelvin scale is -273^{o}C (i.e. 0K)

Charles, a French scientist, discovered that at 0^{o}C, the volume of an ideal gas is 273m^{3}, if the volume reduces to 272m^{3} (i.e. -1m^{3}), the temperature will reduce to -1^{o}C; when the volume reduces to 271m^{3} (i.e. -2m^{3}), the temperature reduces to -2^{o}C. That means at -273^{O}C, the volume of the gas will reduce to 0m^{3} (i.e. the volume vanishes completely at -273^{o}C).

This temperature, -273^{o}C which is the starting point of Kelvin scale is called ** absolute zero. **And the Kelvin temperature is called

*absolute temperature.*0^{o}C = 273K

-273^{o}C = 0K (zero Kelvin)

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