Question

Constants | Periodic Table

A sample of {\rm SO}_{3} is introduced into an evacuated sealed container and heated to 1233 {\rm K}. The following equilibrium is established:

{\rm{2 SO}}_3 {\rm{(}}g{\rm{) }} \rightleftharpoons {\rm{ 2 SO}}_2 {\rm{(}}g{\rm{) + O}}_2 {\rm{(}}g{\rm{)}}.

The total pressure in the system is found to be 3.0 \rm bar and the mole fraction of {\rm O}_{2} is 0.12.

Part A

Find K.

Express your answer using two significant figures.

Answer 1

Solution:-

Mole fraction * total pressure = partial pressure of gas

0.12 mole fraction of O2 x 3.0 atm = 0.36 atm
The mole fraction of SO2 will be twice the mole fraction of O2 since the balanced equation states that 2 moles of SO2 will be obtained for every one mole of O2.
So the mole fraction of SO2 is 2(0.12) = 0.24
Pressure due to SO2 = 0.24 x 3.0 atm = 0.72 atm
The pressure due to SO3 = total pressure minus pressure of SO2 and O2
3.0 atm – (0.36 + 0.72) = 1.92 atm
Kp = (pSO2)^2(pO2) / (pSO3)^2
Kp = (0.72)^2(0.36) / (1.92)^2
Kp = 0.0506