1071712017 11:55 PM A 91.71100 10/1772017 12:48 AM Gradebook Print Calculator Pe

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1071712017 11:55 PM A 91.71100 10/1772017 12:48 AM Gradebook Print Calculator Periadic Table Question 15 of 19 Map General Chemistry 4th Edition University Science Books presented by Sapling Leaming Phosphorus pentachloride decom poses according to the chemical equation K,=1.80 at 250°C A 0.227 mol sample of PCI5(g) is injected into an empty 3.40 L reaction vessel held at 250 °C Calculate the concentrations of PCls(g) and PCl3(g) at equilibrium Number Number PC131 = Previous Give Up & View Solution O Check Answer Next Exit Hint

Explanation / Answer

initially

[PCl5] = mol of PCl5 / volume in L

= 0.227 mol / 3.40 L

= 0.0668 M

[PCl5] [PCl3] [Cl2]

initial 0.0668 0 0

change -1x +1x +1x

equilibrium 0.0668-1x +1x +1x

Equilibrium constant expression is

Kc = [PCl3]*[Cl2]/[PCl5]

1.8 = (1*x)(1*x)/((0.0668-1*x))

1.8 = (1*x^2)/(0.0668-1*x)

0.12024-1.8*x = 1*x^2

0.12024-1.8*x-1*x^2 = 0

This is quadratic equation (ax^2+bx+c=0)

a = -1

b = -1.8

c = 0.1202

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 = 3.721

roots are :

x = -1.864 and x = 6.449*10^-2

since x can't be negative, the possible value of x is

x = 6.449*10^-2

At equilibrium:

[PCl5] = 0.0668-1x = 0.0668-1*0.06449 = 0.00231 M

[PCl3] = 0+1x = 0+1*0.06449 = 0.0645 M

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