Question

In: Chemistry

Consider the following reaction. 2NO2(g)⇌N2O4(g) When the system is at equilibrium, it contains NO2 at a...

Consider the following reaction. 2NO2(g)⇌N2O4(g) When the system is at equilibrium, it contains NO2 at a pressure of 0.722 atm, and N2O4 at a pressure of 0.0521 atm. The volume of the container is then reduced to half its original volume. What is the pressure of each gas after equilibrium is reestablished?

PNO2= ?? atm

PN2O4= ?? atm

Solutions

Expert Solution

P1V1 = P2V2 or P1/P2 = V2/V1 when the volume is reduced to half i.e V2 = 0.5 V1 , P1 / P2 = 0.5 = 1/2

                                                                                                                        P2 = 2 P1

So when the volume is reduced to half, the pressure will be doubled and it is assumed under isothermal condition.

The equation is

                       2 NO2 (g)    N2O4 (g)                    Total P

equillibrium pressure                     0.722 atm          0.0521 atm         0.722 + 0.0521 = 0.7741 atm

Total Pressure = PNO2 + PN2O4

When reducing the volume to half

the total pressure is doubled                  A atm    B atm    2 x 0.7741 = 1.5482 atm

                                                                                                                        A + B = 1.5482 atm

                                                   

Where A and B are the new equillibrium pressure of NO2 and N2O4 respectively

Kp of the reaction at the given equillibrium pressures = [PN2O4] / [PNO2] 2    

                                                                             = 0.0521 / 0.7222 atm-1

                                                                              = 0.1 atm-1

Kp under the new equillibrium conditions is given by

                                                               Kp = B / A2 but Kp = 0.1 atm-1

                     therefore 0.1 = B / A2           but A + B = 1.5482 atm   and hencer B = [1.5482 - A] atm

                                   0.1 = [1.5482 -A]/ A2

                                    01 A2 = 1.5482 - A

                            or   0.1 A2 + A - 1.5482 = 0 This is quadratic equation in A can be solved

                                                                      using the standard formula

                                                     x = [ - b (b2 - 4 ac) ] / 2a

                                 A =[ -1 ( 1 - 4 (0.1)(-1.5482)] / 0.2

                                   The pressure cannot be negative and hence we take only the positive value of .

                                 A =[ -1 + (1.61928) ] /0.2

                                    = [ -1 + 1.2725] / 0.2

                                   = 0.2725/0.2 = 1.3625 atm therefore B = 1.5482 - 1.3625 = 0.1857 atm

PNO2 = 1.3625 atm

PN2O4 = 0.1857 atm

                                 


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