Consider the reaction CH2O (g) ⇌ H2 (g) + CO(g). Exactly 0.040 moles of CH2O were injected into a 250 mL flask. At equilibrium, [CH2O] = 0.057 M. What is Kc for this reaction? Report your answer to the correct number of significant figures.
Step I
Step II
Let x moles of CH2O gets converted into H2 and CO.
At t=0, moles of CH2O = 0.04
Moles of H2 = 0 and Moles of CO = 0
At t=teq, Moles of CH2O = 0.04 - x
Moles of H2 = x and Moles of CO = x
Step III
At t = teq, [CH2O] = 0.057 M
Concentration = Moles / Volume
( 0.04 - x ) / 0.25 = 0.057
x = 0.02575
Step IV
Hence, Moles of H2 = Moles of CO = 0.02575
[H2] = [CH2O] = (0.02575/0.25) = 0.103
Step V
Hence, Kc = (0.103)(0.103) / (0.057)
Kc = 0.186
This is the answer.
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