Question

At 460 degrees celcuis, the reaction SO2(g) + NO2(g) forward and reverse arrows NO(g) + SO3(g) has K= 84.7. All gasses are at an initial pressure of 1.25 atm.

a. Calculate the partial pressure of each gas at equilibrium.

b. Compare the total pressure initially with the total pressure at equilibrium. Would that relation be true of all gaseous systems?

Answer 1

K = pNO * pSO3 / pSO2 * pNO2

84.7 = pNO * pSO3 / pSO2 * pNO2

To get pressures at equilibrium, we make an ICE table:

	SO2(g)	+	NO2(g)	<->	NO(g)	+	SO3(g)
I	1.25		1.25		1.25		1.25
C	-x		-x		+x		+x
E	1.25 - x		1.25 - x		1.25 + x		1.25 + x

84.7 = (1.25 + x)² / (1.25 - x)²

x = 1.00498

Partial pressures in equilibrium:

Gas	Pressure
SO2	0.25 atm
NO2	0.25 atm
NO	2.25 atm
SO3	2.25 atm

The total pressure is the same at the beginning and at the end, however, this is not always the case, as in this case we have a 1 on 1 molar relationship. However, if this relation changes, the relationship of pressures will also change.