Chem 110 Reci – Week 8 – Chemical Equilibrium
Expressing K:
1. Write the expression for the equilibrium constant for the reaction
a. 4NH3(g) + 5O2(g) 4NO(g) + 6H2O(g)
b. 2H2S(g) + 3O2(g) 2SO2(g) + 2H2O(g)
c. Ag2O(s) + 2HNO3(aq) 2AgNO3(aq) + H2O(l)
d. P4(s) + 5O2(g) P4O10(s)
Manipulating K:
1. At 500 K, K for H2(g) + D2(g) 2HD(g) is 3.6. What is the value of K for 2HD(g) H2(g) + D2(g)?
Kr = 1/Kf = 1/3.6 = 0.28
2. At 500 K, Kc for F2(g) 2F(g) is 7.3x10-13. What is the value of Kc for
1/2F2(g) F(g)?
Knew = (Korig)1/2 = (7.3x10-13)1/2 = 8.54x10-7
3. For the reaction N2(g) + 3H2(g) 2NH3(g) at 400 K, K = 41. Find the value of K for each of the following reactions at the same temperature:
a. 2NH3(g) N2(g) + 3H2(g)
Kr = 1/Kf = 1/41 = 0.24
b. 1/2N2(g) + 3/2H2(g) NH3(g)
Knew = (Korig)1/2 = (41)1/2 = 6.4
c. 2N2(g) + 6H2(g) 4NH3(g)
Knew = (Korig)2 = (41)2 = 1681 = 1700
Solving two types of K problems:
Solving for K with concentrations:
1. Haber mixed some nitrogen and hydrogen and allowed them to react at 500 K until the mixture reached equilibrium with the product, ammonia. When he analyzed the equilibrium mixture, he found it to consist of 0.769 M NH3, 0.305 M N2, and 0.324 M H2. What is K for this reaction?
Step 1: 3H2 + N2 2NH3
Step 2:
Step 3:
2. A reaction important in the gasification of coal is
2CO(g) + 2H2(g) CH4(g) + CO2(g)
Determine the equilibrium constant K for this reaction at 298 K, given the following equilibrium concentrations: CO, 4.30x10-9 M; H2, 1.15x10-8 M; CH4, 5.14x10-2 M; CO2, 4.12x10-2 M.
Step 1: Given
Step 2:
Step 3:
3. Determine the equilibrium constant K for 2BrCl(g) Br2(g) + Cl2(g) at 500 K, given the equilibrium concentrations: BrCl, 0.131 M; Br2 3.51 M; and Cl2 0.156 M
Step 1: Given
Step 2:
Step 3:
Solving for K from concentrations:
4. Suppose that the equilibrium molar concentrations of H2 and Cl2 are both 1.0x10-12 M. What is the equilibrium molar concentration of HCl at 500 K, given Kc = 4.0x1018?
Step 1: H2 + Cl2 2HCl
Step 2:
Step 3:
5. Suppose that the equilibrium molar concentration of N2 and O2 in the reaction N2(g) + O2(g) 2NO(g) at 800 K are 0.100 M. What is the equilibrium molar concentration of NO if K = 3.4x10-21 at 800 K?
Step 1: Given
Step 2:
Step 3:
Comparing Q to K:
Q > K too many products (shift towards reactants)
Q < K too many reactants (shifts towards products)
Q = K products equal reactants (at equilibrium)
1. A mixture of H2, N2 and NH3 with molar concentrations 3.0x10-3, 1.0x10-3, and 2.0x10-3 M, respectively, was prepared and heated to 500 K, at which temperature Kc = 62 for the reaction. Decide whether ammonia tends to form or decompose.
Step 1: 3H2 + N2 2NH3
Step 2:
Step 3:
Step 4: Q is larger than K, our reaction will move towards reactants and NH3 will decompose.
2. For the reaction N2O4(g) 2NO2(g) at 298 K, K = 0.98. A mixture of N2O4 and NO2 with initial partial pressures of 2.4 and 1.2 bar, respectively, was prepared at 298 K. Which compound will tend to increase its partial pressure?
Step 1: Given
Step 2:
Step 3:
Step 4: Q is smaller than K, our reaction will move towards products and NO2 will increase its partial pressure.
3. A mixture of hydrogen, iodine, and hydrogen iodide, each at a concentration of 0.0020 M, was introduced into a container heated to 783 K. At this temperature, K = 46 for H2(g) + I2(g) 2HI(g). Predict whether or not more HI has a tendency to form.
Step 1: Given
Step 2:
Step 3:
Step 4: Q is smaller than K, our reaction will move towards products and HI will tend to form.