Chemistry 102
Unit DesignNaleway
Chemical Equilibrium
(Chapter 15)
______|______| | |
Description ApplicationChanging Conditions Chemical Equilibria Qualitative Interpretation LeChatelier’s Principle
Mass Action Expression [Q ] Calculations K and Q Concentration Changes
Equilibrium Constant [K] Predicting Reaction Direction Changing Volume and P
Variation for Q and K Changing Temp
Gas Equilibrium Kc = KpRT-n Catalyst effects
Recommended Practice:
Problems:Ch. 15.All Odd Problems
Outcomes:
1. Understand what is meant by the equilibrium state and how it relates to kinetics
2. Learn to write the mass action expression, Q, and equilibrium constant, K, for all types of equilibria. (homogeneous and heterogeneous)
3. Understand relationship of Q for the forward and reverse reactions
4. Understand relationship between Kc and Kp
5. Understand the qualitative aspects of equilibrium. (what do the values of Qc/ Kc tell us about the reaction)
6. Predict the direction of a reaction by using the reaction quotient, Qc. (Q compared to K -- Reaction Progress)
7. BECOME PROFICIENT AT DOING EQUILIBRIUM CALCULATIONS.
a. Finding equilibrium composition by applying stoichiometry.
b. Obtaining Kc given concentration data
c. Determine equilibrium concentrations from Kc
d Understand the influence of Temperature on the Equilibrium Constant
8. Apply Le Chatelier's Principle for changing conditions. (concentration changes, reactant or product; change in pressure or volume; change in temp; and effects of catalyst)
EquilibriumPractice Problems
- Write the mass action expression for the following equilibrium reactions:
a. N2 (g) + 3 H2 (g) 2 NH3(g); b. 2 N02 (g) N2O4(g)
c. The reaction of black solid copper(II)oxide with hydrogen gas to form copper metal and steams.
2. A mixture of SO2, O2 and SO3 is allowed to reach equilibrium at 852 K. The equilibrium
concentrations are [SO2] = 3.6 x 10-3 mol/L, [O2] = 6.11 x 10-4 mol/ L and
[SO3] = 1.01 x 10-2 mol/L. Calculate Kc for the reaction at this temperature.
2 SO2 + O2 2 SO3
3. At a temperature of 500oC the Kc for 3 H2 (g) + N2 (g) 2 NH3 (g) has a value
of 6.0 x 10-2 L2/mol2. If in a particular vessel at this temperature there are 0.250 M H2 and
0.05 M NH3 present at equilibrium what is the concentration of N2?
Application
4. Nitric oxide is formed at high temperatures from the elements nitrogen and oxygen according
to the reaction a possible nitrogen fixation reaction:
N2 (g) + O2 (g) 2 NO (g) Kc = 0.01 at 2000oC
Predict the direction of this reaction to reach equilibrium at this temperature, if we start with
a. only 1.62 mole N2 and 1.62 mole O2 in a 2 liter container.
b. 4 mole N2, 1.0 mole O2, and 0.8 mole NO in a 20 liter container.
- partial pressure of N2 is 0.2 atm, partial pressure O2 is 0.68 atm, and partial pressure of NO is 0.33 atm. The Kp at this temperature is 1.4.
5. At 440oC Kc = 49.5 for the reaction: H2 (g) + I2 (g) 2 HI (g).
If 0.2 mole hydrogen gas and 0.2 mole of iodine gas are placed in a 10 liter vessel and
allowed to react, what will be the concentration of each substance at equilibrium?
Changing Conditions
6. Predict the general temperature and pressure conditions for the optimum conversion of
ethylene, C2H4, to ethane, C2H6: C2H4(g) + H2 (g) C2H6(g) Ho < 0
What shift in this equilibrium will occur when:
a. more ethylene is added; b. ethane is removed;
c. the volume of the container is decreased d. a catalyst is added.
Answers: 2. 1.3 x 104 3. 2.7 mol/L; 4a. 0, 4b. 0.16, 4c. 0.8;
5. x = 0.016; [H2 and I2 = 4 x10-3 M and HI = 3.2 x 10-2 M]