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Law of Chemical Equilibrium Exercises

Notes on Law of Chemical Equilibrium

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More Goodies:Exercises 9-15!

  1. For each of the following reactions, write an equilibrium law expression. Remember: only aqueous and gaseous molecules/atoms are included in equilibrium expressions.

    2. a. Ag+1(aq) + 2 NH3(g) = Ag(NH3)2+1(aq)

    b. N2O4(g) = 2 NO2(g)

    c. 2 NH3(g) = 3 H2(g) + N2(g)

    d. CH3COOH(aq) = H+1(aq) + CH3CO2-1(aq)

    e. H2O(l) = H+1(aq) + OH-1(aq)

    f. Cu (s) + 2Ag+1(aq) = 2 Ag(s) + Cu+2(aq)

  2. The water gas reaction:

CO2(g) + H2(g) = CO (g) + H2O(g)

was carried out at a constant temperature (900 C) three times with the following results.

Partial Pressure ( treat like concentration in moles/L)

TRIAL Number

CO (g)

H2O(g)

CO2(g)

H2(g)

1

0.352

0.352

0.648

0.148

2

0.266

0.266

0.234

0.234

3

0.186

0.686

0.314

0.314
    1. Write the equilibrium law expression.
    2. Use the data to check if a constant is indeed obtained at 900 C.
  1. Which are more common at equil’m in the following : Reactants ? Or products ?

Cu(s) + Cu+2(aq) = 2 Cu+1(aq) K = 1 X 10–6

4. In Cu(s) + 2 Ag+1(aq) = 2 Ag(s) + Cu+2(aq) at 25 C, there is a lot more Cu+2 than Ag+1 at equilibrium. Which is the only reasonable value for K? ( multiple choice)

A 8.5 X 10-17 B 1.7 X 10-1 C 1.0 X 100 D 2.0 X 10 4
  1. Calculate K for the following reaction at 40 C:

Equation: 2 HI(g) = H2(g) + I2(g)

[HI]eq

[H2(g)]

[I2(g)]eq

4.0 X 10-3

7.5 X 10-3

4.3 X 10-5

 

6. Given : 3 A (g) = 2 B (g) + C (g)

  1. A student introduces 5.0 moles of A into a sealed empty one liter flask at 20 C. When the system reaches equilibrium, only 4.0 moles of A are present. How many moles of B and C are at equil’m?
  2. Calculate K for this reaction at 20 C.
  3. Would a catalyst affect the K value?
  4. Will the catalyst form 2 moles of B faster than without a catalyst?
  5. A student introduces 5 moles of A into an empty 1.0 L flask at a higher temperature. This time, 2.0 moles of A are found at equilibrium. Calculate the new K at this higher temperature.
  6. Was the reaction endothermic or exothermic?

 

7. Given: 2 NH3(g) = 3 H2(g) + N2(g)
  1. In an empty 2.0 L flask kept at a constant temperature, 5.0 moles of NH3 were introduced. Only 1.5 moles of H2 and 0.5 moles of N2 were found at equilibrium. Find K for the above reaction at this specific temperature.
  2. The experiment was repeated at a higher temperature, again with a 2.0 L flask. Four moles of ammonia were used initially and only 1.5 moles reacted. How much nitrogen was formed?

8. Given: 3 A (g) = 2 B (g) + C (g) + heat

  1. After placing 8 moles of A into a sealed empty one litre flask, a student found happiness along with 4.0 moles of B and 2 moles of C. Find K.
  2. The same substances were used in a similar experiment at a different temperature and with a 2.0 L flask. Only 4 moles of A were found at equil’m after starting with 16 moles. Was the temperature lower than that of (a)?

 

Have you ever heard of….

Moronic Acid
This is a triterpenoid organic acid that is found in Pistacia resin, and is therefore of interest to people studying archaelogical relics, shipwrecks and the contents of ancient Egyptian jars. But why it's called moronic acid is still unknown... Derivatives of this are called moronates, as in 'which moron-ate the contents of this jar?'
Ref: P.L. Majumdar, R.N. Maity, S.K. Panda, D. Mal, M.S. Raju and E. Wenkert, J.Org.Chem. (1979) 44, 2811.

Thanks to Dr Ben Stern of Bradford University for supplying this one.