GCHEM please help...Topscore..

future_dentist said:

Well following 2 questions are from Topscore GChem test 1....please post the solution with step by step....I cannot get the solutions....Thank u so much for looking this over...

#56) When 14.250 moles of PCl5 gas is placed in 3L container and comes to equilibrium at constant temp. ; 40.0% of the PCl5 decomposes according to the equation.
PCl5(g) <------> PCl3(g) + Cl2(g)

What is the value of Kc for this rxn?

A) (1.896)^2/2.854
B) (2.854)^2/1.898
C) (3.800)^2/2.854
D) (2.854)(1.896)/3.800

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#62) if the Kb of the solvent is 3.51 C/m and the boiling point of the pure solvent is 70.4 C. Then what is the boiling point of a 4 m solution of a solute dissolved in the solvent.

A) 70.4 L
B) 84.4 L
C) 98.5 L
D) 112.5 L

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Thank u so much for looking over.....

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future_dentist said:

Well following 2 questions are from Topscore GChem test 1....please post the solution with step by step....I cannot get the solutions....Thank u so much for looking this over...

#56) When 14.250 moles of PCl5 gas is placed in 3L container and comes to equilibrium at constant temp. ; 40.0% of the PCl5 decomposes according to the equation.
PCl5(g) <------> PCl3(g) + Cl2(g)

What is the value of Kc for this rxn?

A) (1.896)^2/2.854

First find Molarity 14.25/3= 4.75M
Now 40% decomposes ...meaning your products are each equal to .40(4.75)= 1.9

So 60% percent represents the reactants or .60(4.75)= 2.85

So..... products over reactants = A

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