Question

I am super confused when it comes to these types of questions! Can someone check my work? None of my answers matched those of my teacher when she read them this morning for last night's homework. Please help!

1. Consider the following equilibrium reaction: 2PH3(g) <-> 2P(g) + 3H2(g)
Calculate Keq if it is found that there is 0.70 mols PH3, 0.49 mols P, and 1.2 mols H2 in a 3.0 mL flask.

My work: (1.2/3)^3 * (.49/3)^2/(.70/3>^2 = .03136 rounded .031
Is this right?
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2. When 250f of chlorine is introduced into an evacuated 1.00L flask, it is 25% dissociated into chlorine atoms. Write the reaction and calculate the equilibrium constant. Does the reaction favor reactants or products?

My work:
The reaction is Cl2 <-> 2Cl right?

Then convert grams to moles so 250g/34g = 7.35 moles Cl2

Then the ice chart would be:
For Cl2, I is 7.35, C = 1.84, and E is 5.51
For Cl, I is 0, C is 3.68, and E is 3.68

So the Keq would be (3.68^2)/5.51=2.46
Therefore, it favors products because it is over 1. Is this right?
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3. The equilibrium constant for the reaction Fe2O3(g) + 3CO(g) <-> 2Fe(s) + 3CO2(g) is 2.5. Find the concentration of CO2, if at equilibrium the container has 1.50 mols Fe2O3, 0.75 mols CO, and 3.56 mols Fe.

So I think you don't use the Fe because it is a solid. Therefore:
2.5 = x^3/(1.50)(0.75^3)
So 1.58 = x^3
and x = 1.17 mols
So the concentration of CO2 is 1.17 mols. Is this correct?

Thank you!

Answer 1

For #1. Is that 3 mL? If so then all of the concns are incorrect since moles/LITER is concn. If it should be L, you appear to have done it correctly except that the denominator should be cubed and not squared.
For #2. Looks ok.
For #3. There is no volume listed.