The reaction SO2(g)+2H2S(g)←→3S(s)+2H2O(g) is the basis of a suggested method for removal of SO2 from power-plant stack gases. The standard free energy of each substance are ΔG∘fS(s) = 0 kJ/mol, ΔG∘fH2O(g) = -228.57 kJ/mol, ΔG∘fSO2(g) = -300.4 kJ/mol, ΔG∘fH2S(g) = -33.01 kJ/mol. If PSO2 = PH2S and the vapor pressure of water is 22 torr , calculate the equilibrium SO2 pressure in the system at 298 K.

Answer : The equilibrium pressure is,

Explanation :

The given balanced chemical reaction is,

First we have to calculate the standard free energy of reaction .

where,

= standard free energy of reaction = ?

n = number of moles

Now put all the given values in this expression, we get:

Now we have to calculate the value of

where,

=  standard Gibbs free energy  = -90.72 kJ/mol

R = gas constant = 8.314 J/mole.K

T = temperature = 298 K

= equilibrium constant  = ?

Now put all the given values in this expression, we get:

Now we have to calculate the value of .

The given balanced chemical reaction is,

The expression for equilibrium constant will be :

In this expression, only gaseous or aqueous states are includes and pure liquid or solid states are omitted.

Let the equilibrium pressure be, x

Pressure of = Pressure of = x

Now put all the given values in this expression, we get

Thus, the equilibrium pressure is,

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