Arkansas State University
Department of Chemistry
and Physics
Answers
Equilibria 1

1. Write the equilibrium expression for each of the following:  Where possible, express both Kc and Kp.
 
a)
2 NaN3 (s)
 2 Na (s)   +    3 N2 (g)

b)
4 NH3 (g)  +  5 O2 (g)
 4 NO (g)  +   6 H2O (g)

c)
2 HCl (aq)  + Ca(OH)2 (aq) 
 2 H2O (l)  +  CaCl2 (aq)
2. For equation 1b, would Kc = Kp?  Explain.
No, different number of moles on reactant side and product side.

3. Determine the equilibrium concentrations for each species in the equation:
 
H2 (g)   +    I2 (g) 
 2 HI (g)

 if the initial concentrations of H2 and I2 are 1.0 M and Kc = 54.3 at 430oC.

4. Given the reaction below:
 
H2 (g)   +    I2 (g) 
 2 HI (g)

If the initial concentrations of H2 and I2 are 1.0 M and the initial concentration of HI is 0.5 M (Kc = 54. 3 at 430oC), is the reaction at equilibrium?  If not, which way will the reaction proceed?

Reaction is not at equilibrium, more reactants than should be at euqilibrium, the equilibrium would proceed to the right.

5. According to Le Chatelier's Principle,

a) what effect would the addition of Cl - have on the equilibrium below?
 
CoCl2   +   2 Cl -
 CoCl42-

Shifts the equilibrium to the right, increase in the Cl- concentration creates stress on the reactant side.  To relieve the stress, more CoCl42- is formed.
b) what effect would the addition of Ag+ have on the equilibrium in problem 5a if the Ag+ precipitates as AgCl?
Shifts the equilibrium to the left, the Ag+ ion removes Cl-, to compensate for loss of Cl-, the CoCl42- dissociates to generate more Cl-.