1. for the Following System at Equilibrium

Chemistry Kinetics and Equilibrium 2

1. For the following system at equilibrium: H2 (g) + I2 (g) ↔ 2 HI (g) a. Predict the shift in equilibrium when more HI(g) is added to the system. reactants b. How will the concentration of I2 change? increase

2. For the reaction below, predict the direction the equilibrium will shift given the following changes. Temperature and volume are held constant. 2 NO2 (g) + 7 H2 (g) ↔ 2 NH3 (g) + 4 H2O(g) a. addition of ammonia reactants b. removal of nitrogen dioxide reactants c. removal of water vapour products d. addition of hydrogen products

3. At a particular temperature, the following reaction has an equilibrium constant, Keq of 0.18 PCl3 (g) + Cl2 (g) ↔ PCl5 (g) More PCl3 is added to the system. Will the value of Keq increase or decrease? Neither. Addition or removal of reactants/products does not change Keq

4. The pressure on each of the following systems is increased by decreasing the volume of the container. Explain whether each system would shift in the forward direction, the reverse direction, or stay the same. a. 2 SO2 (g) + O2 (g) 2 SO3 (g) forward

b. H2 (g) + I2 (g) 2 HI(g) neither

c. CaCO3 (s) CaO(s) + CO2 (g) reverse

1+ 1- d. AgCl(s) Ag (aq) + Cl (aq) no effect (no gases present)

5. List three ways that the following equilibrium reaction could be forced to shift to the right:

2 NO2 (g) 2 NO(g) + O2 (g) Add NO2, remove NO or O2, decrease pressure 6. Given the following equilibrium reaction: 2 C(s) + O2 (g) 2 CO(g) what will be the effect of the following disturbances to the system: a. adding CO (at constant volume and temperature) reactants b. addition of O2(at constant volume and temperature) products c. addition of solid carbon (at constant temperature) no effect (solids have no effect) d. decreasing the volume of the container reactants

7. For each of the following equilibrium systems, identify whether the reactants or products are favored at equilibrium, or whether they are equally favored.

-2 a. COCl2 (g) ↔ CO(g) + Cl2 (g) Keq = 8.2× 10 at 627°C reactant 8 b. C(s) + 2 H2 (g) ↔ CH4 (g) Keq = 8.1× 10 at 25°C product

c. PCl5 (g) ↔ PCl3 (g) + Cl2 (g) Keq = 2.24 at 227°C product

33 d. H2 (g) + Cl2 (g) ↔ 2 HCl(g) Keq = 1.8 × 10 at 25°C product

e. C(s) + H2O (g) ↔ CO(g) + H2 (g) Keq = 1.96 at 1000°C product

2+ - -11 f. Mg(OH)2 (s) ↔ Mg aq + 2 OH (aq) Keq = 1.2× 10 at 25°C reactant

8. For each of the following equilibria, predict whether the system will shift in the forward or reverse directions. Note the energy changes involved and assume that the volume remains constant. a. heat is removed from: A B reverse ΔH° = +40.0 kJ b. heat is removed from: A + B 2 C forward ΔH° = -25.5 kJ c. heat is added to: A + 2B 3 C forward ΔH° = -32.0 kJ

You will likely find it easier to answer the question if you first rewrite each equation by including the energy term as part of the equation.

9. In each of the following equilibria, would you increase or decrease the temperature to force the reaction in the forward direction? a. H2 (g) + CO2 (g) H2O(g) + CO(g) Increase ΔH° = +41.0 kJ

b. 2 SO2 (g) + O2 (g) 2 SO3 (g) Decrease ΔH° = -198 kJ

10. For each of the equilibria in Question 2 will the value for Keq increase or decrease if the temperature is raised? Increase, decrease Explain the effect of using a platinum catalyst in the equilibrium reaction of ammonia with oxygen: 4 NH3 (g) + 5 O2 (g) 4 NO(g) + 6 H2O(g) + heat . Answer the following questions based on the potential energy diagram shown here: a. Does the graph represent an endothermic or exothermic reaction? b. Label the postion of the reactants, products, and activated complex. c. Determine the heat of reaction, ΔH, (enthalpy change) for this reaction. 50 d. Determine the activation

energy, Ea for this reaction. 200 e. How much energy is released or absorbed during the reaction? 50 f. How much energy is required for this reaction to occur? 50 overall, 200 to start

11. Sketch a potential energy curve that is represented by the following values of ΔH and Ea. You may make up appropriate values for the y-axis (potential energy).

ΔH = -100 kJ and Ea = 20 kJ Is this an endothermic or exothermic reaction?

12. In the next unit we will be discussing reactions that are reversible, and can go in either the forward or reverse directions. For example, hydrogen gas and oxygen gas react to form water, but water can also be broken down into hydrogen and oxygen gas. We typically write a reaction that can be reversed this way, using the double arrow symbol ( or ↔):

2 H2 + O2 ↔ 2 H2O This reaction is exothermic in the forward direction:

2 H2 + O2 ↔ 2 H2O + 285 kJ but endothermic in the reverse direction:

2 H2O + 285 kJ ↔ 2 H2 + O2 Consider a general reversible reaction such as: A + B ↔ C + D

13. Given the following potential energy diagram for this reaction, determine ΔH and Ea for both the forward and reverse directions. Is the forward reaction endothermic or exothermic?

Exo, delta H = -20 forward, 20 reverse, Ea forward = 60, Ea reverse = 80

14. Sketch a potential energy diagram for a general reaction A + B ↔ C + D Given that ΔHreverse = -10 kJ and Ea forward = +40 kJ

15. We have typically been simplifying our potential energy curves somewhat; for multistep reactions, potential energy curves are more accurately shown with multiple peaks. Each peak represents the activated complex for an individual step. Consider the PE curve for a two-step reaction:

a. What is ΔH for the overall reaction? -20

b. What is ΔH for the first step of the reaction mechanism? 20

c. What is ΔH for the second step of the reaction mechanism? -40

d. What is ΔH for the overall reverse reaction? 20

e. What is Ea for the first step? 80

f. What is Ea for the second step? 40 g. Which is the rate-determing step - step 1 or step 2? How do you know? 1, it is slower

h. What is Ea for the reverse of step 1? 60 i. Is the overall reaction endothermic or exothermic? exo