SS 1 CHEMISTRY

SS 1 CHEMISTRY

Lesson 2

TOPIC: The kinetic theory of gases

There are two types of gases, namely:

1. Ideal gases
2. 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:

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

VARIABLES USED FOR DISCRIBING GAS BEHAVIOURS

1. Volume
2. Pressure
3. 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 (m³). The practical units of volume are the cubic centimetre (cm³), cubic decimetre (dm³) and the litre (L). the cubic centimetre is equivalent to millilitre (ml).

1L = 1dm³ = 1000cm³ = 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 (^oC). another SI unit of temperature is the Kelvin (K). The starting point of Celsius scale is the freezing point of water at 0^oC while the starting point of Kelvin scale is -273^oC (i.e. 0K)

Charles, a French scientist, discovered that at 0^oC, the volume of an ideal gas is 273m³, if the volume reduces to 272m³ (i.e. -1m³), the temperature will reduce to -1^oC; when the volume reduces to 271m³ (i.e. -2m³), the temperature reduces to        -2^oC. That means at -273^OC, the volume of the gas will reduce to 0m³ (i.e. the volume vanishes completely at -273^oC).

This temperature, -273^oC which is the starting point of Kelvin scale is called absolute zero. And the Kelvin temperature is called absolute temperature.

0^oC = 273K

-273^oC = 0K (zero Kelvin)

 

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