Question

If PSO2 = PH2S and the vapor pressure of water is 21 torr , calculate the equilibrium SO2pressure in the system at 298 K.
Express your answer using one significant figure.

Answer 1

The balanced equation is

SO2 (g) + 2 H2S (g) <--------> 3S(s) + 2 H2O(g)

=> Assume that the partial pressure of sulfur dioxide, P(SO2), is equal to the partial pressure of dihydrogen sulfide, P(H2S), and therefore P(SO2) = P(H2S).

=> If the vapor pressure of water is 21 torr, calculate the equilibrium partial pressure of SO2 P(SO2) in the system at 298 K.

=> convert the given pressure of water to atm, which is: 0.0276 atm.
=> We know that Kp is 8.0*10¹⁵

Kp=P(H2O)²/P(SO2)P(H2S)²

what i did: 8.0*10¹⁵ = (0.0276)²/x³

8.0*10¹⁵ x x3=2.1x10^-5

x³=2.1*10^-5/8.0*10¹⁵
x³= 2.625x10^-21
x = cube root of 2.625x10^-21  
x = 1.379 x 10^-7

The equilibrium SO2 pressure in the system at 298K=1.379 x 10^{-7 .}