Practice with Chemical Equilibrium (Chapter 14)
(Due 2/17)
Here are four additional practice exercises concerning chemical equilibrium (Chapter 14).
See your instructor if you have questions. Note that for these questions, the symbol "=" is
used to indicate a reversible reaction. Your textbook uses a double-headed arrow.
1. Suppose that equal molar amounts of PCl3 and Cl2 are added to a 2.00 L vessel at 250
o
C. The two reagents react to form PCl5 according to the reaction below:
PCl3 + Cl2 = PCl5
At equilibrium, 0.0173 mol of PCl5 are present and the total gas pressure is 2.00 atm.
What is the reaction's equilibrium constant?
2. K has a value of 50.0 at 448 oC for the reaction H2 + I2 = 2 HI. If 45 g of H2 and 95 g
of I2 are placed in a 25 L container, what will be the equilibrium concentrations of H2,
I2, and HI?
3. The gas-phase reaction below has a negative enthalpy of reaction for the forward
direction.
4 HCl + O2 = 2 H2O + 2 Cl2
Predict the result of each of these changes to this reaction at equilibrium.
(a) Temperature increase
(b) Volume decrease
(c) Addition of krypton
(d) Addition of a catalyst
(e) Pressure decrease
(f) Removal of water with a desiccant
4. Chemistry students sometimes study the reaction of ethanol (EtOH) and acetic acid
(HAc) to form water and ethyl acetate (EtAc). Suppose you have this reaction already
at equilibrium with the following concentrations:
[EtOH] = 0.67, [HAc] = 0.67,
[EtAc] = 1.33, and [H2O] = 1.33.
(a) Calculate the equilibrium constant K.
(b) Now suppose that the equilibrium is perturbed by adding 2.00 more moles of
acetic acid. Calculate the values of all four concentrations once the new equilibrium is
established.
Practice with Chemical Equilibrium (Chapter 14) ADDENDUM
(Due 2/17)
5. An unknown concentration of Acetic Acid (Ka = 1.8 x 10-5) results in a solution with
pH 3.62. What are [H+], [A-], [HA]eq, [HA]initial, pOH?
Hint: calculate [HA]initial before [HA]eq.
6. An upset tummy has a pH of 1.5 and a volume of 0.50 L. If the person takes a
1000 mg table of Vitamin C (98% ascorbic acid, C6H8O6, Ka = 8.0 x 10-5) and the
tummy equilibrates, what will the pHtummy be?
How many Vitamin C tables would be required to adjust pHtummy to 1.25?
Assume that the original pH in the tummy was due to a strong acid and that no other
chemicals are involved.