CHM 2046C Module 10 Sample Exam Answers

Part E: Experimental Determination of Equilibrium Constants 10 points

Calculate the equilibrium constant at 25^oC for the reaction:

2 NOCl(g) ç è 2 NO (g) + Cl₂ (g)

when 2.00 moles of NOCl were placed in a 1.00-L flask, and the concentration of NO after equilibrium was achieved was 0.66 moles/liter.

	[NOCl(g)]	[NO (g)]	[Cl2 (g)]
Initial M	2.00 M	0	0
Change	-0.66 M	+ 0.66 M	+½∙(0.66 M)
Equilibrium M	1.34M	0.66 M	0.33M

[NO]² [Cl₂]¹

K_c = -------------------

[NOCl]²

[0.66]² [0.33]¹

K_c = ------------------- = 0.80

[1.34]²

McMurray describes how to write equilibrium expressions from the equilibrium reactions in Chapter 13 section 13.1. Then he demonstrates how to calculate the Equilibrium constant from the equilibrium concentrations. See worked Example 13.2 page 502. Then try Problem 13.2 page 502. Try problems 13.50, 13.51, 13.52, 13.53, 13.54 p 536.

Kotz 6^th Reference section 16.3 p 770-772 See Example 16.3 p771 using K_c and Example 16.4 using K_p and Partial pressures. Try Exercise 16.5 p772; then go to the end of the chapter on page 790 and try #7-#12. The Solutions manual for these exercises have been distributed.

On the next page is a worked example from another text: