1.1 What is Chemistry?

http://www.ck12.org Chapter 19. Chemical Equilibrium

• Equilibrium constants allow us to predict the relative amounts of reactants and products for a given chemical
  process.


• The equilibrium constant depends on the temperature at which the reaction is taking place, but it does not
  depend on the initial (pre-equilibrium) concentrations of the reactants and products.

Lesson Review Questions

1. Write the equilibrium constant expression (Kc) for each of the following processes:
   (a) 2O 3 (g)3O 2 (g)
   (b) 3O 2 (g)2O 3 (g)
   (c) 2NO(g)+Cl 2 (g)2NOCl(g)


2. The equilibrium constants for three different reactions are shown below. Are these reactions reactant-favored
   or product-favored?
   (a) 4.64× 10 −^3 at 25°C
   (b) 2.2× 10 −^10 at 100°C
   (c) 150 at 25°C


3. Write the pressure-based equilibrium constant expression (Kp) for the following reaction: N 2 (g)+3H 2 (g)
   2NH 3 (g). If Kp=4.3× 10 −^3 for the forward reaction, calculate Kpfor the reverse reaction. (Hint: Write the
   equilibrium constant expression for the reverse reaction. How is it related to the expression for the forward
   reaction?)


4. The equilibrium constant for the following reaction is equal to 1.74× 10 −^5 : CH 3 CO 2 H(aq) +H 2 O(l)
   CH 3 CO− 2 (aq) +H 3 O+(aq). Would you expect there to be more CH 3 CO 2 H or more CH 3 CO 2 −present after
   this reaction reaches equilibrium?


5. What is the value of Kcfor the following reaction: 2A+BC? The equilibrium concentrations of A, B, and
   C are [A]=1.64 M, [B]=1.84 M, and [C]=0.45 M.


6. 2.34 moles of A and 1.17 moles of B are introduced into a 3.8 L vessel. They are allowed to react until the
   following process reaches equilibrium: 2A+BC. At equilibrium, 0.52 moles of A are present. What is the
   value of Kcfor this reaction?

Further Reading / Supplemental Links

1. Chemical equilibria simulation: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/animationsind
   ex.htm


2. NO 2 /N 2 O 4 equilibrium experiment: Teresa Anderson Curtin, Darryl Wahlstrom, McCormick James Journal
   of Chemical Education 1991 68 (9), 781

Points to Consider

• Given that the chemical equilibrium for all chemical reactions is temperature dependent, how do you suppose
  temperature influences a given chemical equilibrium?


• Can you think of chemical processes that may be reactant-favored at one temperature and product-favored at
  another?


• Can you think of other factors that may influence whether or not a given chemical process is reactant-favored
  or product-favored?