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Gas Laws Notes

April 20, 2013

Introduction to gas laws notes:

The state of a gas is a function of its pressure, volume and temperature. If we study the variation of one of these quantities with respect to another quantity keeping the remaining quantity constant, we obtain gas laws. Boyle’s law is one of the gas laws that shows the variation of pressure with volume, keeping temperature constant. Charles’ laws are the laws that show the variation of volume with temperature, keeping pressure constant and the variation of pressure with temperature, keeping volume constant. Let us see the notes of different gas laws.

gas laws notes : Boyle’s Law

Statement :  It states that At a given temperature, the pressure of a given mass of a gas is inversely proportional to its volume.

If P is the pressure of a certain mass of a gas and V is its volume at a temperature T K then

P  `prop` `(1)/(V)`   ( T constant )

P   =  `(K)/(V)`

`PV = K` .

Where k is a constant for a given mass of a gas and at a given temperature. k changes with the mass of the gas and its temperature. Boyle’s law is applicable for an ideal or a perfect gas. But real gases obey it at low pressures and high temperatures.

gas laws notes : Charles’ Law

While experimenting with balloons, Jacques Charles,  a French physicist, found that equal volumes of all ordinary gases expand by the same amount for the same amount for the same rise of temperature provided that the pressure remains constant. This led to the Charles’ , law at constant pressure

(i)  Charles Law at Constant Pressure

Statement :  At constant pressure, the volume of a given mass of a gas is directly proportional to its temperature on Kelvin scale.

If V is the volume of a given mass of a gas at a temperature T K then by Charles’ law at constant pressure

V `prop`  T  (P constant)

V  =  kT

`(V)/(T)`  = k

where k is a constant for a given mass of a gas and at a given pressure. k varies with the mass of the gas and its pressure.

 

(ii) Charles’ Law at Constant Volume    :    Charle’s law at constant volume is also known as Gay-Lussac’s law.

Statement :  It states that At constant volume, the pressure of a given mass of a gas is directly proportional to its temperature on Kelvin scale.

If P is the pressure of a given mass of a gas at a temperature T K, then by Charles’ law at constant pressure of Gay-Lussac’s law

P  `prop`   T  ( V constant )

P  =  k T

`(P)/(T)`  = k

where k is a constant for a given mass of a gas and at a given volume. k varies with the mass of the gas and its volume.

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