Wednesday, April 17, 2013

Standard gas volume

Introduction :
Each gas is characterized by the property of volume.  Volume is a space occupied by a gas. Volume is dependent on the temperature.  More the temperature more would be the volume.  Standard gas volume is defined as volume occupied by a gas at standard temperature and pressure.

 What are the figures for standard pressure and temperature?  The figures of standard pressure and temperature are adopted at 1 atmosphere and 273 degree Kelvin.  For the gas loss, the value of the units of pressure and temperature are always taken as atmosphere and degree kelvin.  The volume occupied by a gas at these standard conditions is called as standard volume.

Equations to find standard gas volume

Boyle established the relationship between pressure and the volume.Charles established the relation between pressure and temperature.
From both of these equations the universal gas law equation was derived and from the same ideal gas law equation was derived.
The ideal gas law equation is PV =nRT, here 'P' is pressure, 'V' is volume, 'n' is number of moles, 'R' is the gas constant and 'T' is temperature.  If the values for standard pressure and temperature are substituted at 1 atmosphere and 273 degree kelvin, the volume occupied by 1 mole of a gas comes to 22.4 liters.
Thus 22.4 liters is a standard volume of 1 mole of any gas.  This equation was derived by Avogadro. He quantified the volume occupied by 1 mole of gas at standard conditions

Illustration to show standard gas volume

The standard volume has been useful to find many other things in practical chemistry.Let us consider following problems.

Problem 1:
                   Find volume occupied by 64 grams of oxygen at STP
                                                       Or
                       Find the standard volume of 64 gms of oxygen.

Answer:  64 no. of moles of oxygen is = 64 / 32 = 2.
               If 1 mole occupies 22.4 litres, 2 moles would occupy 44.8 liters.

Problem 2:
                   Find the moles of the gas if the standard volume is 100 liters.

Answer: 1 mole occupies 22.4 liters,
             so 100 liters is occupied by 100 / 22.4 = 4.464 moles.

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