Download In_Class_Practice Chapter 17 PreAP

Practice Work: Section 17.1 A State of Dynamic Balance
Example Problem 1 - Equilibrium Constant Expressions for Homogeneous Equilibria
Write the equilibrium constant expression for the reaction of hydrogen sulfide and water vapor to form sulfur dioxide and
hydrogen.
H2S(g) + 2H2O(g)  SO2(g) + 3H2(g)
Practice Problems
1. Write equilibrium constant expressions for the following homogeneous equilibria.
a. C2H4O(g)  CH4(g) + CO(g)
b. 3O2(g)  2O3(g)
c. 2N2O(g) + O2(g)  4NO(g)
d. 4NH3(g) + 3O2(g)  2N2(g) + 6H2O(g)
Example Problem 2 - Equilibrium Constant Expressions for Heterogeneous Equilibria
Write the equilibrium constant expression for the high-temperature reaction of carbon dioxide and solid carbon to form
carbon monoxide.
CO2(g) + C(s)  2CO(g)
Practice Problems
2. Write equilibrium constant expressions for the following heterogeneous equilibria.
a. C4H10(l)  C4H10(g)
b. NH4HS(s)  NH3(g) + H2S(g)
c. CO(g) + Fe3O4(s)  CO2(g) + 3FeO(s)
d. (NH4)2CO3(s)  2NH3(g) + CO2(g) + H2O(g)
Example Problem 3 - Calculating the Value of Equilibrium Constants
Nitrogen monoxide and bromine react to form nitrosyl bromide according to the following equation.
2NO(g) + Br2(g)  2NOBr(g)
Calculate Keq for this equilibrium using the data [NOBr] = 0.0474 mol/L, [NO] = 0.312 mol/L, and [Br2] = 0.259 mol/L.
Practice Problems
3. The following is the chemical equation for the decomposition of formamide.
HCONH2(g)  NH3(g) + CO(g)
Calculate Keq using the equilibrium data [HCONH2] = 0.0637 mol/L, [NH3] = 0.518 mol/L, and [CO] = 0.518 mol/L.
4. Hydrogen and carbon disulfide react to form methane and hydrogen sulfide according to this equation.
4H2(g) + CS2(g)  CH4(g) + 2H2S(g)
Calculate Keq if the equilibrium concentrations are
[H2] = 0.205 mol/L, [CS2] = 0.0664 mol/L, [CH4] = 0.0196 mol/L, and [H2S] = 0.0392 mol/L.
5. The equilibrium constant is 9.36 for the following reaction.
A(g) + 3B(g)  2C(g)
The table below provides concentration data for two different reaction mixtures of these gases. Can you conclude that both
reactions are at equilibrium? Explain your answer.
Mixture 1
Mixture 2
A
0.716
0.562
Concentrations (mol/L)
B
0.208
0.491
C
0.425
0.789
Practice Work: 17.2 Factors Affecting Chemical Equilibrium
Practice Problems
6. Use Le Châtelier’s principle to predict how each of the following changes would affect this equilibrium.
C2H4O(g)  CH4(g) + CO(g)
a. adding CH4(g) to the system
b. removing CO(g) from the system
c. removing C2H4O(g) from the system
7. How would decreasing the volume of the reaction vessel affect these equilibria?
a. CO(g) + H2(g)  H2CO(g)
b. NH4HS(s)  NH3(g) + H2S(g)
c. 2NbCl4(g)  NbCl3(g) + NbCl5(g)
d. 2SO3(g) + CO2(g)  CS2(g) + 4O2(g)
8. Phosphorus pentachloride decomposes exothermically to form phosphorus trichloride and chlorine.
PCl5(g)  PCl3(g) + Cl2(g) + heat
How would you regulate the temperature of this equilibrium in order to do the following?
a. increase the concentration of PCl5
b. decrease the concentration of PCl3
c. increase the amount of Cl2 in the system
d. decrease Keq
9. Predict how this equilibrium would respond to a simultaneous decrease in both temperature and pressure.
N2O4(g)  2NO2(g) H° = +58 kJ
17.3 Using Equilibrium Constants
Example Problem 4 - Calculating Equilibrium Concentrations
At 350°C, Keq = 66.9 for the formation of hydrogen iodide from its elements.
What is the concentration of HI if [H2] = 0.0295 mol/L and [I2] = 0.0174 mol/L?
H2(g) + I2(g)  2HI(g)
Practice Problems
10.
At a certain temperature, Keq = 0.118 for the following reaction.
2CH4(g)  C2H2(g) + 3H2(g)
Calculate these concentrations.
a. [CH4] in an equilibrium mixture with [C2H2] = 0.0812 mol/L and [H2] = 0.373 mol/L
b. [C2H2] in an equilibrium mixture with [CH4] = 0.726 mol/L and [H2] = 0.504 mol/L
c. [H2] in an equilibrium mixture with [CH4] = 0.0492 mol/L and [C2H2] = 0.0755 mol/L
11.
A chemist studying the equilibrium N2O4(g)  2NO2(g) controls the temperature so that Keq = 0.028. At one
equilibrium position, the concentration of N2O4 is 1.5 times greater than the concentration of NO2. Find the concentrations of
the two gases in mol/L. (Hint: Let x = [NO2] and 1.5x = [N2O4] in the equilibrium constant expression.)
Calculations with Equilibrium Constants (ICE Tables)
1. Sulfur trioxide decomposes at high temperature in a sealed container. Initially the vessel is charged at 1000 K with SO3(g)
at a concentration of 0.500 mol/L. At equilibrium the concentration of SO3 is 0.200 mol/L. Calculate the value of Keq at 1000
K.
2SO3(g)
⇆
2SO2(g)
+
O2(g)
2. For the following reaction the equilibrium constant, Keq, has the value 4.97x10-5 at 500 K. A gas cylinder at 500 K is
charged with PCl5(g) at an initial concentration of 1.66 mol/L. What are the equilibrium concentrations of PCl5, PCl3, and Cl2 at
this temperature?
PCl5(g)
⇆
PCl3(g)
+
Cl2(g)
3. A container initially holds 1.00 mol/L of NO2. If Keq is 6.67 x 10-5 at 530oC, what is the equilibrium concentration of O2 at
this temperature?
2NO2(g)
⇆
2NO(g)
+
O2(g)
4. The reaction in problem 3 is repeated but this time the container initially held 1.00 mol/L of NO2 AND 2.00 mol/L of NO.
What is the equilibrium concentration of O2? (How do you think this will compare to the answer to problem 3?)
5. A container initially holds 37.3 mol/L of NO. If Keq is 3.445 at 530oC, what is the equilibrium concentration of O 2 at this
temperature?
2NO(g)
⇆
N2(g)
+
O2(g)
6.
Calculate the equilibrium constant, Keq, for the following reaction at 25 °C, if [NO]eq= 0.106 M, [O 2]eq= 0.122 M and
[NO2]eq= 0.129 M.
2 NO (g)
+
O2 (g)
↔
2NO2(g)
7. Find the equilibrium constant, Keq, for the following equilibrium. The initial concentrations of AB and A 2D are 0.30 M
before they are mixed and when equilibrium is reached, the equilibrium concentration of A 2D is 0.20 M. Use an ICE table
for your calculation.
2 AB (g)
+
C2D (s) ↔
A2D
(g)
+
2 CB (s)
8.
If 0.50 mol of NO2 is placed in a 2.0L flask to create NO and O2, calculate Equilibrium concentration if K eq =1.2 x 10-5
2 NO (g)
+
O2 (g)
↔
2NO2(g)
9.
For the system, if we start with 0.100mol/L of CO2 and H2, what are the concentrations of the reactants and products at
equilibrium given that Keq= 0.64 at 900K?
CO2 (g)
+ H2 (g)
↔
CO (g)
+
H2O (g)
10. For the system, if we start with 0.010 mol/L of both H2 and I2 and 0.096 mol/L of HI, what are their concentrations at
equilibrium given that Keq= 0.016?
2HI(g)
↔
H2 (g)
+
I2 (g)
11. At 650°C, the reaction below has a Keq value of 0.771. If 2.00 mol of both hydrogen and carbon dioxide are placed in a
4.00 L container and allowed to react, what will be the equilibrium concentrations of all four gases?
H2 (g)
+ CO2 (g)
↔
CO(g)
+ H2O (g)
12. Carbonyl bromide, COBr2, can be formed by reacting CO with Br2. A mixture of 0.400 mol CO, 0.300 mol Br2, and 0.0200
mol COBr2is sealed in a 5.00L flask. Calculate equilibrium concentrations for all gases, given that the Keq= 0.680.
CO (g)
+
Br2 (g)
↔
COBr2 (g)
Example Problem 5 - Calculating Molar Solubility and Ion Concentration from Ksp
The Ksp for lead(II) fluoride (PbF2) is 3.3x10-8 at 25°C. Use this Ksp value to calculate the following.
a. The solubility in mol/L of PbF2
b. The fluoride ion concentration in a saturated solution of PbF 2
Practice Problems
12.
Use the data in Table 17.3 in your textbook to calculate the
solubility in mol/L of these ionic compounds at 298 K.
a. MgCO3
b. AlPO4
c. Ag2SO4
d. Al(OH)3
13.
Use the data in Table 3 in your textbook to calculate the following ion concentrations at 298 K.
a. [Ba2+] in a saturated solution of BaCrO4
b. [CO32-] in a solution of ZnCO3 at equilibrium
c. [Cl-] in a solution of PbCl2 at equilibrium
d. [Mg2+] in a saturated solution of Mg3(PO4)2
Example Problem 6 - Predicting a Precipitate
Predict whether a precipitate will form if 200 mL of 0.030M CaCl2 is added to 200 mL of 0.080M NaOH. A double-replacement
reaction might occur according to this equation.
CaCl2 + 2NaOH  2NaCl + Ca(OH)2
14.
Use Ksp values from Table 3 in your textbook to predict whether a precipitate will form if equal volumes of these
aqueous solutions are mixed.
a. 0.010M Ba(NO3)2 and 0.050M Na2SO4
b. 0.020M KBr and 0.015M Pb(NO3)2
c. 0.0060M Na2CrO4 and 0.0025M AgNO3
15.
Will a precipitate form when 125 mL of 0.010M K2SO4 is mixed with 250 mL of 0.015M CaBr2? (Hint: Note that the
volumes of the two solutions are not equal, and the volume after mixing is 375 mL.)