Chapter 4 – Summary

aA + bB + cC ... equilsymbol.gif (859 bytes) ... + xX + yY + zZ, the expression will be

Review

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

In the following problems, calculate any numerical answer to three significant figures.

1. K was first determined empirically by Guldberg and Waage.  What does this mean?
  a) They calculated it from an understanding of equal forward and reverse reaction rates.
  b) They tried different variations of mathematical calculations on the experimentally determined equilibrium concentrations for several reactions, until they found one that was constant.
  c) They set up an experiment to measure the reaction of hydrogen and iodine.
  d) None of the above is correct. 

2. K should never be written without also including the balanced equilibrium reaction, because the same equation can be properly balanced using different coefficients.   Different ways of balancing result in different numerical values of K.
  True        False

3. Which of the following is a correct K expression for the equation it represents?

  a)   2NO2 (g) equilsymbol.gif (859 bytes) N2O4 (g)
  b)   BaSO4 (s) Ba2+ (aq) + SO42- (aq) sum_002_02.gif (411 bytes)
  c)   CO2 (g) + 4 H2 (g) CH4 (g) + 2 H2O (g) sum_002_03.gif (451 bytes)
  d)   3H2 (g) + H2 (g) 2NH3 (g)
  e)   (NH4)2S (s) 2NH3 (g) + H2S (g)
  f) none of the above is correct

4. Here are some values of K for the reaction: CaCO3 (s) Ca2+ (aq) + CO32- (aq) at different temperatures:

T (oC) Ksp
25 3.31 x 10-9
35 2.82 x 10-9
45 2.42 x 10-9
55 2.10 x 10-9

This reaction is:
  a) Endothermic        b) Exothermic

5. In an IRE table, which is the only row that is affected by the coefficients in the balanced equation?
a) I       b) R       c) E

6. Some textbook authors refer to the concept of an IRE table, as an "ICE" table.  Given the meaning of "R" in the "IRE" table, which of the following makes the most sense for the meaning of "C"?
a) concentration       b) change      c) calculation     d) calorimetry

7. At a certain temperature, a container filled with PCl3, Cl2 and PCl5 gases is in equilibrium.  The concentrations of each substance at equilibrium are found to be:

Gas Concentration (mol/L)
PCl3 0.185
Cl2 0.385
PCl5 0.015

What is the value of K for the reaction PCl3 (g) +  Cl2 (g) PCl5 (g)?
 

8. You have to calculate the value of K for the reaction Ca(OH)2 (s) Ca2+ (aq) + 2 OH- (aq).  At equilibrium you have found experimentally that the concentration of OH- (aq) ions when calcium hydroxide is dissolved in water is 1.05 x 10-2 mol/L.  What is the value of K?
  Note: enter numbers in scientific notation (i. e. 1.23 x 10-3 as 1.23E-3).

9. 0.100 mol of H2, 0.300 mol of I2, and 0.200 mol of HI   gases are placed in a 1.00 L flask and heated until the reaction has reached equilibrium.  After equilibrium has been reached the concentration of I2 (g) is 0.212 mol/L.  What is K for the reaction H2 (g) + I2 (g) 2HI (g) at this temperature?
 

10. The equilibrium constant for the reaction of the Haber process, N2 (g) + 3H2 (g) 2NH3 (g) is Kc = 0.100 at 500 K.  If the concentration of N2 and H2 are both = 0.0100 M at equilibrium, then what is the concentration of NH3 at this temperature?
 

11. In the reaction 2NO2 (g) N2O4 (g) at 75 ºC, Kc = 6.93.  If you put 0.0200 mole of NO2 into a 1 L container, and allowed it to reach equilibrium, how much NO2 and N2O4 would you have?   Hint: set this problem up so that you can do an iterative solution.
[NO2] =       [N2O4] =

12. At 450 ºC, Kc = 1.89 x 10-2 for the decomposition of hydrogen iodide, 2HI (g) H2 (g) + I2 (g).  In an experiment, 0.435 g of HI is placed in a 2 litre flask, and then heated to 450 ºC and allowed to reach equilibrium.

a) What is the initial concentration of HI? 

b) What is the final concentration of HI?    

13. Equal amounts of PCl3 (g) and Cl2 (g) are heated in a container to 550 K.  At this temperature the value of Kc = 0.413 for the reaction PCl3 (g) + Cl2 (g) PCl5 (g).  If the concentration at equilibrium of PCl5 (g) is 2.40 x 10-3 mol/L, then what are the concentrations of PCl3 (g) and Cl2 (g) at this temperature?
 

14. In a titration to measure the amount of Ca(OH)2 that dissolves in a saturated solution, 24.20 mL of the saturated solution of calcium hydroxide is required to titrate 16.04 mL of 0.0500 M HCl.  What is the concentration of hydroxide ions, OH-, in the saturated solution?
  a) 1.66 x 10-2        b) 3.31 x 10-2       c) 6.63 x 10-2        d) 30.17         e) none of the above