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Boyles Law Formula

Boyle’s Law, an ideal gas law which states that the volume of an ideal gas is inversely proportional to its absolute pressure at a constant temperature. The law applies only to ideal gases which allow only pressure and volume to change.


In other words, the product of pressure and volume is constant for a fixed mass of ideal gas at fixed temperature.


                                          P1 X V1 = P2 X V2


The other way to express Boyle’s Law is as follows





  •    P denotes pressure of the gas
  •    V denotes volume of the gas
  •    K is constant and holds units of force times and distance.


Example 1

Neon (Ne) sample occupies 4L at a pressure of 5 x 104 Pa and 273K temperature. Calculate the volume of the sample at STP?




Initial conditions are

P1 = 5 x 10-4Pa and V1 = 4L


Final conditions are

P2 = 101325 Pa and V2 = ?


We have an equation

P1 x V1 = P2 x V2

V2 = P1V1/P2

V2 = (5 x 104 Pa) (4L) / 1.01325 x 105 Pa

     = 2 x 10 5 / 1.01325 x 105 L


Hence, V2 = 1.97 L



Example 2

A gaseous nitrogen sample in a 65L air bag has a pressure of 745 mm Hg. If this sample is transferred into a 25 L bag at same temperature, what is the pressure of the gas in 25L bag?




Initial conditions

P1 = 745 mm of Hg and V1 = 65L


Final conditions

V2 = 25L and P2 =?


We have an equation


P1V1 = P2V2


Put the above values in this equation

P2 = P1V1/V2

P2 = 745 mm of Hg x 65L / 25L


Therefore P2 = 1940 mm Hg


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