m/ibiscms/mod/ibis/view.php?id-4796032 Chemical Equ 8/2018 11:55 PM 4 83.8/1002/

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m/ibiscms/mod/ibis/view.php?id-4796032 Chemical Equ 8/2018 11:55 PM 4 83.8/1002/8/2018 01:15 PM Print Calculator-d Periodic Table Gra stion 15 of 25 Incorrect IncorrectIncorrectIncorrectIncorrect Map eneral Chemistry 4th Edition University Science Books presented by Sapling Learning Phosphorus pentachloride decomposes according to the chemical equation PCI Kc= 1.80 M at 250°C A 0.348 mol sample of PCIs(g) is injected into an empty 3.80 L reaction vessel held at 250 . Calculate the concentrations of PCls(g) and PCl3(g) at equilibrium Number PC151= 1.2069 Number [PCI,1-11.2985 | M Previous Give Up & View Solution e Check Answer +1 Exit Next

Explanation / Answer

initial concentration of PCl5 = number of mol of PCl5 / volume in L
= 0.348 mol / 3.80 L
= 0.0916 M

ICE Table:

                    [PCl5]              [PCl3]              [Cl2]             

initial             0.0916              0                   0                 

change              -1x                 +1x                 +1x               

equilibrium         0.0916-1x           +1x                 +1x               

Equilibrium constant expression is
Kc = [PCl3]*[Cl2]/[PCl5]
1.8 = (1*x)(1*x)/((0.0916-1*x))
1.8 = (1*x^2)/(0.0916-1*x)
0.16488-1.8*x = 1*x^2
0.16488-1.8*x-1*x^2 = 0
This is quadratic equation (ax^2+bx+c=0)
a = -1
b = -1.8
c = 0.1649

Roots can be found by
x = {-b + sqrt(b^2-4*a*c)}/2a
x = {-b - sqrt(b^2-4*a*c)}/2a

b^2-4*a*c = 3.9

roots are :
x = -1.887 and x = 8.736*10^-2

since x can't be negative, the possible value of x is
x = 8.736*10^-2

At equilibrium:
[PCl5] = 0.0916-1x = 0.0916-1*0.08736 = 0.00424 M
[PCl3] = +1x = +1*0.08736 = 0.08736 M

Answer:
[PCl5] = 0.00424 M
[PCl3] = 0.0874 M

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