Chapter 3 – Summary

Review

Try the following review questions to check your understanding of the concepts in this chapter.

1. Which of the following correctly identifies the initial response to the applied stress?

Applied Stress

le Châtelier's Principle Prediction of Response to Stress
Reactants + energy Products
Increase T Decrease
Increase T Decrease
Decrease T Decrease
Decrease T Decrease

Potassium dichromate2. The color intensity of a saturated solution of potassium dichromate (there is some solid at the bottom of the beaker) does not appear to change, even if some more solid is added.   Which of the following statements is correct?
  a) There is no change in color because the solubility reaction is not an equilibrium system.
  b) There is no change in color because adding more solid changes the surface area, but not the concentration of the solid state.
  c) Adding solid potassium dichromate increases the concentration of dichromate ions, but it is cancelled by a decrease in the concentration of the water.
  d) None of the above is correct. 

3. What will happen to the pressure in this system if the temperature is increased?

CaCO3 (s) + energy    CaO (s) + CO2 (g)

  a) The reaction will shift to the left, so the pressure will decrease.
  b) The reaction will shift to the right, so the pressure will increase.
  c) Because the reaction involves solids, there will be no effect.

4. What would happen in the following reaction: CO (g) + NO2 (g) CO2 (g) + NO (g) if the volume of the container is decreased?
  a) The pressure will increase, so the reaction will shift to the left, forming more CO2 (g) + NO (g)
  b) The pressure will increase, so the reaction will shift to the right, forming more CO (g) + NO2 (g)
  c) The pressure will decrease, so the reaction will shift to the left, forming more CO2 (g) + NO (g)
  d) The pressure will decrease, so the reaction will shift to the right, forming more CO (g) + NO2 (g)
  e) There will be no effect.

5. What would happen in the following reaction: PCl5 (g) PCl3 (g) + Cl2 (g) if the volume of the container is increased?
  a) The pressure will increase, so the reaction will shift to the left, forming more  PCl5 (g)
  b) The pressure will increase, so the reaction will shift to the right, forming more PCl3 (g) + Cl2 (g)
  c) The pressure will decrease, so the reaction will shift to the left, forming more  PCl5 (g)
  d) The pressure will decrease, so the reaction will shift to the right, forming more PCl3 (g) + Cl2 (g)
  e) There will be no effect.

6. Which of the following would provide common ions for the reaction:

AgCl (s)   Ag+ (aq) + Cl- (aq)


  NaNO3      KCl       AgCl       AgNO3

7. Which of the following correctly identifies the effect of adding some solid AgCl to a saturated solution of AgCl (s) dissolved in water?

Le Châtelier's Principle Prediction of Response to Stress
AgCl (s) Ag+ (aq) +  Cl- (aq)
Increase Decrease Decrease
Decrease Increase Increase
Decrease Decrease Increase
No Change Decrease Decrease
No Change No Change No Change

8. Which of the following correctly identifies the effect of adding some solid NaCl to a saturated solution of AgCl dissolved in water?

Le Châtelier's Principle Prediction of Response to Stress
AgCl (s) Ag+ (aq) +  Cl- (aq)
Increase Decrease Decrease
Decrease Increase Increase
Decrease Decrease Increase
No Change Decrease Decrease
No Change No Change No Change

9. In a saturated solution of PbCl2, the concentration of Cl- (aq) ions at equilibrium is about 3.6 x 10-2 mol/L.  Suppose that 1 x 10-2 mol of NaCl was dissolved in 1 L of this solution.  Then the concentration of Cl- (aq) ions would be:
a) unchanged at 3.6 x 10-2
b) the original amount of Cl- from the dissolved PbCl2, plus the 1 x 10-2 mol/L from the NaCl, for a total of 4.6 x 10-2
c) the 1 x 10-2 mol/L from the NaCl, with no contribution from the PbCl2, for a total of 1 x 10-2
d) the 1 x 10-2 mol/L from the NaCl, plus a decreased amount of Cl- (less than 3.6 x 10-2 mol/L) from the PbCl2 for a total of about 4.2 x 10-2

10. Consider the following equilibrium involving gases:

N2O4 (g) 2NO2 (g)

If some He, an inert gas, was added to the container that contains the above gases, then the total pressure would increase so:
a) the reaction would shift to the left.
b) the reaction would shift to the right.
c) there would be no change.