COOP IV                                                                     ________________________

Chem 1403-40                                                                                     (name)

Dr. Robert E. Belford

 

 

1.    Does the following reaction favor reactants or products?

                        2SO3(g)  -->  2SO2(g)  +  O2(g)   K =  7.9 x 10-9

 

Reactants, K is a very small fraction

 

 

2.  Calculate the equilibrium constant Kc for the reaction

                        PCl3(g) + Cl2(g)  -->  PCl5(g)

when a mixtures of the gasses has the following equilibrium concentrations

 

[PCl3]  =  2.4 x 10-2,   [Cl2]  =  8.9 x 10-2,   [PCl5] =  3.7 x 10-2  

 

 

 

 

 

3.  Using the results from question 2, determine Kc for the following reaction.

 

                                    PCl5(g)   -->  PCl3(g) + Cl2(g)

 

 

 

 

4.  Using the results from question 2, determine Kp for the following reaction at 25 deg C.

                                    PCl3(g) + Cl2(g)  -->  PCl5(g)

 

 

 

 

 

 

 

 

 

 

5.  Consider the following equilibrium:

                        2HI(g) <==>  H2(g)  +  I2(g)  

 

At equilibrium a 5.00 L vessel contains 4.50 mol I2, 4.50 mol H2 and an unknown amount of HI.  Kc for this equilibrium is 0.0183.  What is the equilibrium concentration of HI?

 

 

 

 

 

 

6.  For the reaction H2(g)  +  I2(g)  -->  2HI(g),  DHo = -9.4kJ,  for each of the following changes, will the equilibrium product concentration increase or decrease?

 

a.  Addition of hydrogen                      Increase

b.  Removal of Iodine                          Decrease

c.  Increase in Pressure                       No Effect

d.  An increase in Temperature           Decrease

 

 

 

7.  For the reaction  2NF3 (g) à N2(g)  +  3F2(g)  ,  DHo = +4.3kJ/mol,  for each of the following changes, will the equilibrium product concentration increase or decrease?

 

a.  Addition of Fluorine                       Decrease

b.  Removal of Nitrogen                      Increase         

c.  Increase in Pressure                       Decrease

d.  An increase in Temperature           Increase

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

8.  Consider the reaction

 

            2SiO(g) <==> 2Si(l) + O2(g);  Kc = 9.62 x 10-1

 

If 1.00 mol SiO is placed into a 1.00 L container, what are the equilibrium concentrations of  all species?

 

 

                                    2SiO(g)    <==>     2Si(l)    + O2(g)

Initial moles:               1                                  0          0

Change:                       -2x                               +x        +x

Equil. Conc.                [1-2x]              (constant)        [x]

 

 

The first answer is nonsense, so [O2] = 0.247M & SiO=0.506M

 

 

9.  Calculate the value of the equilbrium constant for the reaction

 

                                    2NO(g)  +  O2(g)  <==>  N2O4(g)                    K = ?

 

Knowing the following equilibrium constants at the same Temperature and Pressure

 

            2NO(g)  +  O2(g)  <==>  NO2(g)                     K1 =  2.0 x 102

 

            N2O4(g) <==>  2 NO2(g)                                 K2 = 7.2 x 10-4

 

Writing the second one backward makes it the reciprocal of the forward, then adding coupled equations makes the coupled equilibrium constant multiplicative

 

 

 

 

 

 

 

 

10.   A mixture of 0.659 g of H2 and 26.7 g Br2 is heated in a 3 L container. These substances react as follows

                                                H2(g)  +  Br2(g)  <==>  2HBr(g)

At equilibrium the vessel is found to contain 10.4 g of Br2.  Calculate Kc for this reaction

 

 

 

 

                                    H2(g)  +           Br2(g)    <==>  2HBr(g)

[Initial]:                       .110                 0.0557                         0

Change:                       -x                     -x                                 2x

[Equilibrium]:             .11-x                .0557-x                        2x

                                                            [0.0217]

From Bromine data:  0.0217 = 0.0557-x  =>  x  = 0.036

So [H2]eq = 0.11 – 0.026 = 0.084   and   [HBr]eq = 2(0.036) = 0.072

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

11.  Given the reaction:

                                                Cl2(g)  + 2HBr(g)   çè  Br2(g) +  2HCl(g)

70.9g of chlorine is mixed with 161.8g of HBr in a 10.0 L vessel.  What are the equilibrium concentrations of all species if Kc = 1.5 x 101? 

The initial molarity of chlorine is 70.9g(70.9g/mol)/10L=0.100M

The initial molarity of hydrogen bromide is 161.8g(80.9g/mol)/10L=0.200M

 

                                    Cl2(g)  + 2HBr(g)   çè  Br2(g)  <==>  2HCl(g)

Initial moles:               .1              .2                            0                      0

Change:                       -x             -2x                           +x                    +2x

Equil. Conc.                [.1-x]      [.2-2x]                      [x]                   [2x]

 

 

[Cl2]= .1-.0712 = 0.0288M

[HBr] = .2-2(0.0712) = 0.0576M

[Br2]=.0712

[HCl] = 2(0.0712) = 0.142M

 

12.   Calculate the equilibrium constant if one mole of pure ethyl alcohol is mixed with one mole of pure acetic acid at room temperature.  The products are ethyl-methyl ester  and the equilibrium mixture contains 2/3 moles of the ester.

                        C2H5OH  +  CH3OOH  ç è  H2O  +  H3CCOOCH2CH3 

Initial moles:               1               1                             0                      0

Change:                       -x             -x                             +x                    +x

Equil. moles                [1-x]     [1-x]                          [x]                   [x]

X=2/3, 1-X=1/3

EquilConc:                  [1/3]/V   [1/3]/V                     [2/3]/V                        [2/3]/V