1. Consider a fire burning in a fireplace. Is equilibrium established? Explain.
  1. which if the following are equilibrium situations? Explain your answer in each case. (a) During a football game, 22 players are on the field and the rest are on the bench. (b) the student population of your high school is constant over a period of five years. (c) The mercury vapor in a thermometer when a temperature is constant. (d) A glass of iced tea, which has undissolved sugar at the bottom of it after being stirred for half an hour. There is no ice remaining. (e) Today, during school hours, 15 percent of the students at your school are in physical education class. (Disregard before and after school hours.) (f) A well-fed lion in his cage. The lion’s weight is constant.
  1. One drop of water may or may not establish a state of vapor-pressure equilibrium when placed in a closed bottle. Explain.
  1. What do the following experiments (done at 25 degrees C) show about the state of equilibrium (a) One liter of water is added, a few milliliters at a time, to a kilogram of salt, which only partly dissolves. (b) A large saltshaker containing 1 Kg of salt is gradually emptied into 1 liter of water. The same amount of salt dissolves as in (a).
  1. Consider the following reaction at equilibrium:

4NH3(g) + 5 O2(g)  4NO(g) + 216.4 kcal

(a) When equilibrium is attained, what observations concerning macroscopic (observable) properties could you make? Be specific. (b) Describe what is happening on the molecular level at equilibrium. (c) With the temperature and volume held constant, more NH3(g) is added to the system. When equilibrium is reestablished, what will be the equilibrium concentrations of each substance compared to what they were before the NH3, how would you change (increase or decrease) each of the following? (I) temperature of the system; (ii) pressure of the system; (iii) partial pressure of H2O(g); (iv) partial pressure of NO(g); (v) partial pressure of O2(g).

6.Consider the reaction for the manufacture of water gas which you studied is Chapter 9: c(s) + H2O(g)  CO(g) + H2(g)

H = +31.4 kcal

Which of the following will increase the equilibrium yield of products? (a) Removing some of the H2O using a dehydrating agent. (b) Increasing the temperature of the system. (c) Increasing the pressure on the system. (d) Removing the products as they are formed. (e) Using powdered instead of lump coal.

7.When some of the NO2-N2O4 mixture shown in Figure 11-4 is placed in a syringe at room temperature, the following is observed: as the piston is gradually pushed in, the red brown color of NO2 first darkens and the becomes progressively lighter. It always, however, remains darker than it was originally. The equation for the equilibrium is N2O4(g)  2NO2(g) H = +14.1 kcal

colorlessred-brown

Explain the experimental results, using Le Chatelier's principle.

8.Everyone knows that water expands when it freezes into ice. Will putting ice under pressure cause it to melt? Explain, using Le Chatelier's principle.

  1. Explain, using Le Chatelier's principle, why increasing the pressure on boiling water causes it to stop boiling until a higher temperature is reached. The equation is:

H2O (l)  H2O (g) H = +9.7 kcal/mole

  1. Each of the following reactions has come to equilibrium. What will be the effect on

the equilibrium concentration (increase, decrease, no change) of each substance in the system when the change described below is made?

a) 2H2(g) + 2NO(g)  N2(g) + 2H2O(g) The pressure on the system is increased

b) SO2(g) + .5O2(g)  SO3(g) + 23 kcal The temperature is increased

c) P4(g) + 6H2(g)  4PH3(g) H2(g) is added

d) FeO(s) + CO(g)  Fe(s) + CO2(g)

The Fe(s) is removed as rapidly as it is formed

e) N2(g) + O2(g)  2NO(g) The pressure on the system is increased

  1. Write the equilibrium law expression for each of the following reactions:

a)N2(g) + 2O2(g)  2NO2(g)

b)2C(s) + 3H2(g)  C2H6(g)

c)NaOH(s) + H+(aq)  Na+(aq) + H2O(l)

d)I2(s)  I2(aq)

  1. Write the equilibrium law expression for each of the following reactions:

a)3O2(g)  2O3(g)

b)MgCO3(s)  MgO(s) + CO2(g)

c)SO2(g) + NO2(g)  SO3(g) + NO(g)

d)2Bi3+(aq) + 3H2S(g)  Bi2S3(s) + 6H+(aq)

  1. Given that K = 5.0 x 10-5 for the reaction 2NO(g) + O2(g)  2NO2(g) Calculate the equilibrium concentration of oxygen gas if the NO and NO2 concentrations are known to be equal at equilibrium. (Concentrations are given in moles liter.)
  1. Given the reaction at equilibrium 2A + BC + 3D

Calculate the value of K if the equilibrium concentrations are found to be:

[A] = 10.0 M[B] = 15.0 M

[C] = 5.0 M[D] = 25.0 M

  1. Reactants A and B are mixed, each initially at a concentration of 1.0 M. They react slowly to produce C according to the equation 2A + BC

When equilibrium is established the concentration of C is found to be 0.30 M. Calculate the value of K.

  1. Consider the reaction described by the following equation:

H2(g) + CO2(g)  H2O(g) + CO(g)

One mole of H2(g) and one mole of CO2(g) are allowed to react in a 1-litre container until equilibrium is attained. If the equilibrium concentration of H2 is 0.44 M, what is the equilibrium of each of the other substances?

  1. In the reaction Fe2+(aq) + Ag+(aq)  Fe3+(aq) + Ag(s) at equilibrium the following concentrations were found: [Fe2+] = 0.50 M ; [Ag+] = 1.0 M ; [Fe3+] = 1.50 M. ( a ) Calculate the equilibrium constant, K, for the reaction. ( b ) If at equilibrium the concentration of Fe2+(aq) is found to be 0.20 M and the concentration of Ag+(aq) is 0.30 M, what must be the concentration of Fe3+(aq)?
  1. Select from each of the following pairs the more random system. ( a ) Your room just after you have cleaned it and your room a week later. ( b ) A beaker just before and just after you have dropped it. ( c ) Logs stacked in your fireplace and their combustion products after burning. ( d ) A cube of sugar before and after being dropped into hot coffee.
  1. Consider the reaction Y(s) + 2W(g)  2Z(s) H = -200 kcal

( a ) Which reaction (forward or reverse) is driven by the tendency toward minimum energy? ( b ) Which reaction is driven by the tendency toward maximum randomness?

  1. For each of the following reactions, state (I) whether the tendency toward minimum energy favors reactants or products; (II) whether the tendency toward maximum randomness favors reactants or products.

a)CO(g) + ½O2(g)  CO2(g)

H = -67.6 kcal

b)Mg(s) + ½O2(g)  MgO(s)

H = -146 kcal

c)NaCl(s)  NaCl(aq)

H = +0.4 kcal

d)H2SO4(aq)  H2SO4(l)

H = +19.0 kcal

e)Pb2+(aq) + 2I-(aq)  PbI2(s)

H = -14.0 kcal

f)Br2(s)  Br2(l)

H = +16.2 kcal

  1. For each of the following reactions, state (I) whether the tendency toward minimum energy favors reactants or products; (II) whether the tendency toward maximum randomness favors reactants or products.

a)3C2H2(g)  C6H6(g)

H = -142.6 kcal

b)H2(g) + F2(g)  2HF(g)

H = -128.5 kcal

c)CS2(g) + 3O2(g)  CO2(g) + 2SO2(g)

H = -265 kcal

d)NaOH(s)  NaOH(aq)

H = -10.2 kcal

e)CO2(g)  CO2(aq)

H = -4.8 kcal

f)C3H8(l)  C3H8(g)

H = + 83.6 kcal