Question

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At a certain temperature and total pressure of 1.2 atm, the partial pressures of an equilibrium mixture for: 2A (g) <---> B (g))

are Pa = 0.60 atm and Pb= 0.60 atm. After a disturbance, the system regains the equilibrium with a total pressure of 1.7 atm. What is the partial pressure of A at the new equilibrium?

=_____ atm

Answer 1

The given equilibrium is

Partial pressures of the gases at equilibrium are

Hence, the equilibrium constant Kp can be calculated as

Now, a disturbance is made to the previous equilibrium and the sum of the partial pressures after regaining the equilibrium is

Note that since the reaction has reached the new equilibrium, its equilibrium constant Kp will be the same again.

Hence, we now have two equations and two variables to solve for at the new equilibrium.

Hence, putting the value of Pb in equation (2) in equation (1), we get

Now, we can solve the above quadratic equation in variable Pa to get the equilibrium partial pressure of Pa at the new equilibrium suing the quadratic formula

For a quadratic equation

the solution for x is

Hence, for our equation.

We know that the partial pressure can not be negative. Hence, the correct equilibrium partial pressure of A is about 0.75 atm.