GENERAL GAS EQUATION, SI-UNITS OF GENERAL GAS CONSTANT (R), DENSITY OF AN IDEAL GAS, REAL GAS OR NON-IDEAL GAS, LIMITATIONS OF REAL GAS FROM IDEAL BEHAVIOUR

 

GENERAL GAS EQUATION:

 

            In gas laws different parameters are constant i.e;

 

Boyle’s law                 (at constant temperature)

Charles Law               (at constant pressure)

Avogadro’s law         (at constant temperature and pressure)

By combining the three gas law. We get such an equation in which all the three parameters are variable. Mathematically;

 

V                  (Boyle’s law)

 

V  T              (Charles law)

V n               (Avogadro’s law)

 

On combining;

 

            V     

 

            V = T   

Where ‘R’ is the universal gas constant or ideal gas constant or molecular gas constant.

 

R =

PV = nRT

 

Or

 

This is called general gas equation for ideal gas.

 

            PV = nRT

 

As, mole =  or n =

By substituting this value;

 

            PV =  RT

 

            Mr =                     

 

SI-UNITS OF GENERAL GASCONSTANT (R):

 

                        R =

            SI-units of a gas at s.t.p .

 

                        P = 1 atom = 101325 Nm^-2.

V = 22.4 dm3 = 0.0224 m³.

n = 1 mole

T = O 0C + 272 = 272K

            R = 101225 x 0.0224                        Nm-2. M3

                            1 x 273                          mole . k   

= 2269.868    N.m K^-1 mole^-1.

        273

R = 8.31 JK-1 mole-1

 

 

            Similarly, SI-units of a gas at r.r.p.

 

                        p = 1 atom = 101325 Nm^-2

                        v = 24 dm³ = 0.024 m³

                        n = 1 mole

                        t = 20 ⁰C + 273 = 293 K

                        R = 101325 x 0.024              Nm-2. m3

                                      1 x 293                             mole k

 

                        R = 2431.8     N.m K^-1 mole^-1

                                  293

 

R = 8.31 JK-1 mole-1

 

 

 

DENSITY OF AN IDEAL GAS:

 

            General gas equation for an ideal gas;

                        PV = nRT

            As        n =  RT

           

                        M =

                        PV =  RT

 

                        M =                                             

            As        d =  or m = d x v

                        D x V =                                                     

d =

 

 

 REAL GAS OR NON-IDEAL GAS:

 

            Some gases at some conditions do not obey the gas laids and the ideal gas equation are called real gases or non ideal gases.

 

LIMITATIONS OF REAL GAS FROMIDEAL BEHAVIOUR:

 

            Real gases deviate from ideal behavior. In order to understand the non ideal behavior of real gases let us consider a graph of real gases which is drawn at different temperature by taking pressure on x-axis and the factor on  y-axis.

           

                        PV = nRT

= 1

           

Or       

 

            Hence, when pressure of a gas is increased at a constant temperature, the volume of the gas is decreased in such a way  that product of  should remain one. Thus for an ideal gas the group is a straight horizontal line.