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Introduction to Charles Law Formula

Charles Law Definition

Charles’ Law describes the relationship between volume and temperature of gases.

 This law is named for Jacques Charles, who studied the relationship volume, V, and temperature, T, around the turn of the 19th century.

 He determined that for the same amount of a gas at constant pressure,

                           V / T  = constant

 This defines a direct relationship whcih means an increase in one results in an increase in the other. 

What Does Charles’ Law Mean?

   V / T = constant

Suppose we have a cylinder with a piston allowing volume to change, and a heating/cooling element allowing for changing temperature.  The force on the piston head is constant to maintain pressure, and the cylinder is contained so the amount of gas is constant.

An increase in temperature results in increased volume.

Conversely, when the temperature decreases, volume decreases.

 

Charles' Law Formula


Charles’ Law can be used to predict the interaction of temperature and volume.     

If we know the initial temperature and volume, and have a target value for one of those variables, we can predict what the other will be for the same amount of gas under constant pressure.

    V1 / T1 = V2 / T2

        V1 = initial volume

        T1 = initial temperature

        V2 = final volume

        T2 = final temperature

 If we know three of the four, we can calculate the fourth.


Application of Charles' Law Formula

V1 / T1 = V2 / T2

V1 = 2.5 liters

 T1 = 250 K

 V2 = 4.5 liters

 T2 = ?

     Solving for T2, the final temperature equals 450 K.

 So, increasing the volume of a gas at constant pressure from 2.5 to 4.5 liters results in a temperature increase of 200 K.

Summary

  • Volume / Temperature = Constant
  •   V1 / T1 = V2 / T2
  •   With constant pressure and amount of gas, we can use these relationships to predict changes in temperature and volume.