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# CIE A-levels Chemistry watch

1. Hydrogen and carbon dioxide gases are mixed at 800K. A reversible reaction takes place.
H2(g) + CO2(g)==> H2O(g) + CO(g)
At equilibrium, the partial pressures of H2 and CO2 are both 10.0 kPa. Kp is 0.288 at 800K.
What is the partial pressure of CO in the equilibrium mixture?
A 5.37 kPa B 18.6 kPa C 28.8 kPa D 347 kPa

Answer scheme says it's A. Can someone please show me the working?
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3. Kp= (partial pressure of CO x parital pressure of H20) / (partial pressure of CO2 x partial pressure of H2

• Since the moles of CO2 and H2 are same, and they have equal partial pressures, we assume that the partial pressures of the two products will also be same since they too have the same number of moles

So,
Kp = p(CO) x p(H2O) / p(CO2) x p(H2)
0.288= (p x p) / 10 x 10
0.288= p^2 / 100
0.288 x 100= p^2
28.8 = p^2
_/28.8 = _/p^2
5.366 = p
p ~ 5.37kPa

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Updated: November 14, 2017
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