A sample of iron(II)sulfate was heated in an evacuated container to 920 K, where the following reactions occur:
2FeSO4(s) ↔ Fe2O3(s) + SO3(g) + SO2(g)
SO3(g) ↔ SO2(g) + ½ O2(g)
At equilibrium the total pressure is 0.836 atm and the partial pressure of oxygen was 0.0275 atm. Calculate Kp for both reactions.
I answer this before, so I'm gonna answer again. Step by step.
1) Based on the 1: 1 stoichiometry of the first reaction,
PSO3 = PSO2
call this value 'x'
2) After the second reaction finishes, at equilibrium we know the following:
the PSO3 value has gone down from that
produced by reaction 1 (because some SO3 produced by
reaction 1 was used up)
the PSO2 has gone up from that produced in
reaction 1 (because some SO2 was made, in addition to
that made in reaction 1)
3) Since we know PO2 at equilibrium to be 0.0275 atm:
PSO3 = x - 0.0275
PSO2 = x + 0.0275
4) The sum of all three equilibrium pressures is 0.836 atm:
(x - 0.0275) + (x + 0.0275) + 0.0275 = 0.836
x = 0.40425 atm
5) Kp for the first reaction is:
Kp = (PSO3) (PSO2)
Kp = (0.40425) (0.40425) = 0.163
5) Kp for the second reaction is:
Kp = [ (PSO2) (PO2)1/2 ] / (PSO3)
Kp = [(0.43175) (0.0275)1/2] / (0.37675) = 0.190
Hope this helps
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