Charles Law - States of Matter, CBSE, Class 11, Chemistry PDF Download

CHARLES LAW FORMULA

Charles’ law is one of the gas laws which explains the relationship between volume and temperature of a gas. It states that when pressure is held constant, the volume of a fixed amount of dry gas is directly proportional to its absolute temperature. When two measurements are in direct proportion then any change made in one of them affects the other through direct variation. Charles’ Law is expressed by the equation:

Or

Where,

V1 and V2 are the Initial Volume and Final Volume respectively. T1 refers to the Initial Temperature and T2 refers to the Final Temperature. Both the temperatures are in the units of Kelvin.

Jacques Charles, a French scientist, in 1787, discovered that keeping the pressure constant, the volume of a gas varies on changing its temperature. Later, Joseph Gay-Lussac, in 1802, modified and generalized the concept as Charles’s law. At very high temperatures and low pressures, gases obey Charles’ law.

Derivation:

Charles’ Law states that at a constant pressure, the volume of a fixed mass of a dry gas is directly proportional to its absolute temperature. We can represent this using the following equation:

Since V and T vary directly, we can equate them by making use of a constant k.

The value of k depends on the pressure of the gas, the amount of the gas and also on the unit of the volume.

VT = k ———– (I)

Let V1 and T1 be the initial volume and temperature of an ideal gas. We can write equation I as:

 ———– (II)

Let’s change the temperature of the gas to T2. Consequently, its volume changes to V2. So we can write,

 ———– (III)

Equating equations (II) and (III),

Hence, we can generalize the formula and write it as:

Or

You know that on heating up a fixed mass of gas, that is, increasing the temperature, the volume also increases. Similarly, on cooling, the volume of the gas decreases. At 0 degree centigrade, the volume of the gas increases 1/273 of its original volume for a unit degree increase in temperature.

It is to be noted here that the unit Kelvin is preferred for solving problems related to Charles’ Law, and not Celsius. Kelvin (T) is also known as the Absolute temperature scale. For converting a temperature to Kelvin scale, you add 273 to the temperature in the centigrade/Celsius scale.

Charles’ Law in Real Life:

Charles’ law has a wide range of applications in our daily life. Some of the common

Examples are given below:

• In cold weather or environment, balls and helium balloons shrink. 
• In bright sunlight, the inner tubes swell up.