Ch 17 Review Answers 9-16

9. Which of the following reactions is homogeneous? (Multiple Choice)

a.   Zn(s) + HCl(aq) «ZnCl₂(aq) + H₂(g)

b.   CaCO₃(s) + HCl(aq) « CO₂(g) + CaCO(s) + H₂O(l) 

c.   CO(g) + NO₂(g) « CO₂(g) + NO(g) (all substances are the same state of matter)

10.  Explain how dissolving a slightly soluble salt to form a saturated solution is an equilibrium process.

        Only a small amount of a slightly soluble salt will dissolve. When the solution is saturated equilibrium is established. The total amount of solid dissolved remains constant, but at the surface of the solid, ions are going into solution at the same rate other ions are reforming into a solid.

11. List 3 catalysts from lecture, the book, or previous labs.

      Enzymes, carbonic anhydrase, Cl in ozone depletion, FeCl₃, MnO₂

12. Explain how Freon breaks down ozone in the upper atomosphere.

      The decomposition of Freon (CF₂Cl₂) releases Cl atoms. The Cl atoms combine with  O₃ to form ClO and O₂. An O atom combines with the ClO to produce Cl and O₂. The Cl atom is now free to break up another ozone molecule at a rate of 1 million per second.

13. Equilibrium can only be achieved in a __closed__ system. One with a lid, stopper, cap, etc.

14. Draw a picture representing carbon dioxide dissolved in Coke solution when pressure is on the system (it has a cap), and after the pressure is released (the cap is removed.)

In the capped bottle of Coke, CO2(aq) is dissolved in the solution. Trapped above the soda and cap, the CO2 is gaseous and remains at equilibrium with the aqueous CO2 dissolved in the Coke.

In the capped bottle, aqueous CO2 is dissolved in the Coke, but any gaseous CO2 existing above the Coke is released into the atmosphere and equilibrium does not occur. Gradually, all the aqueous CO2 escapes the solution to become gaseous CO2, and that’s how Coke goes flat.

15. Of the four changes that can shift equilibrium (pressure, volume, and temperature), which is the only one that will shift K? _____temperature______________

16. Draw and label the equilibrium diagram Figure 17.10 on p. 547. Describe what is happening in the diagram over time.

At first, the rate of the forward reaction decreases and the rate of the reverse reaction increases. Equilibrium is reached when the forward rate and the reverse rate become the same.