In: Chemistry
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
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