Name___________________________________________
Equilibrium Worksheet
C(s) + CO2(g) ⇌ 2 CO(g)
(2008)
1. Solid carbon and carbon dioxide gas at 1,160 K were placed in a rigid 2.00 L ontainer,
and the reaction represented above occurred. As the reaction proceeded, the total pressure
in the container was monitored. When equilibrium was reached, there was still some C(s)
remaining in the container. Results are recorded in the table below.
Time(hours)
Total Pressure of Gases in
Container at 1,160 K (atm)
0.0
2.0
4.0
6.0
8.0
10.0
5.00
6.26
7.09
7.75
8.37
8.37
(a) Write the expression for the equilibrium constant, Kp , for the reaction.
(b) Calculate the number of moles of CO2(g) initially placed in the container. (Assume
that the volume of the carbon is negligible)
(c) For the reaction mixture at equilibrium at 1,160 K, the partial pressure of the CO2(g)
is 1.63 atm. Calculate
(i)
the partial pressure of CO(g) , and
(ii)
the value of the equilibrium constant, Kp .
(d) If a suitable solid catalyst were placed in the reaction vessel, would the final total
pressure of the gases at equilibrium be greater than, less than, or equal to the final
total pressure of the gases at equilibrium without the catalyst? Justify your answer.
(Assume that the volume of the solid catalyst is negligible.)
In another experiment involving the same reaction, a rigid 2.00 L container initially
contains 10.0 g of C(s), plus CO(g) and CO2(g) , each at a partial pressure of 2.00
atm at 1,160 K.
(e) Predict whether the partial pressure of CO2(g) will increase, decrease, or remain the
same as this system approaches equilibrium. Justify your prediction with a calculation.
(2011)
2. Each of three beakers contains 25.0 mL of a 0.100 M solution of HCl, NH3 , or NH4Cl,
as shown above. Each solution is at 25°C.
(a) Determine the pH of the solution in beaker 1. Justify your answer.
(b) The value of Kb for NH3(aq) is 1.8 × 10−5 at 25o C.
(i) Write the equation for the base equilibrium reaction that occurs
(ii)Write the Kb expression for the reaction of NH3(aq) with H2O(l).
(iii) Calculate the [OH-] in the solution in beaker 2. Justify your answer
(c) The value of Ka for NH4+ (aq) is 5.6x10-10 at 25o C.
(i) Write the equation for the acid equilibrium reaction that occurs
(ii)Write the Ka expression for the reaction of NH4+(aq) with H2O(l).
(iii) Calculate the pH of the solution in beaker 3. Justify your answer
3. 2 H2S(g) ⇌ 2 H2(g) + S2(g)
When heated, hydrogen sulfide gas decomposes according to the equation above.
Initially, only 3.40 g sample of H2S(g) is introduced into an evacuated rigid 1.25 L
container. The sealed container is heated to 483 K. When equilibrium is reached,
3.7210-2 mol of S2(g) is present at equilibrium.
(a) Write the expression for the equilibrium constant, Kc, for the decomposition
reaction represented above.
(b) Based on the information in the statement above and the stoichiometry of the
chemical reaction, determine the equilibrium concentration, in molL-1, of the
following gases in the container at 483 K. You cannot get this correct without the
use of an “ICE” table.
2 H2S(g)
(i)
H2(g)
(ii)
H2S(g)
⇌
2 H2(g)
+
S2(g)
(c) Based on your expression in (a) and all equilibrium concentrations, calculate the
value of the equilibrium constant, Kc, for the decomposition reaction at 483 K.
4. Hypobromous acid, HOBr, is a weak acid that dissociates in water. The Ka of
hypobromous acid is 2.3 x 10-9.
(a) Write the dissociation equation and Ka expression.
(b) Calculate the value of [H+] in a 1.34 M HOBr solution.
(c) Calculate the concentration of HOBr (aq) in a pure HOBr solution that has [H+] =
1.8 x 10-5 M.
(d) What would happen to the equilibrium if sodium hydroxide were added? Explain
how approximately equal volumes of equal concentration weak acid could
neutralize a strong base.
5. C6H5NH2, Aniline a weak base, reacts with water.
(a) Predict the equation and write the equilibrium expression Kb for the reaction.
(b) A sample of aniline is dissolved in water to produce 25.0 mL of a 0.10 M
solution. The pH of the solution is 8.82. Calculate the equilibrium constant, Kb,
for this reaction.
(c) What would the pH of a 1.0 M solution of aniline be?
(d) What effect would adding hydrochloric acid have on the [C6H5NH3+]? Justify
your answer.