CHM 2046C Module10 Name:___________

Chapter 13 McMurry Homework Packet

Module Ten: Chemical Equilibria Chapter 13

Possible

Actual

 

A. Equilibrium Constant Derivation from Reaction Rates Lecture

5

 

 

B. Writing Equilibrium Constant Expressions

5

 

 

C. Meaning of the Equilibrium Constant: K;

5

 

 

D. Meaning of the Equilibrium Quotient: Q;

5

 

 

E. Determination of Equilibrium Constants from Lab Data

10

 

 

F. La Chatelier's Principle Problems

10

 

 

G. Determination of Equilibrium Conc from Kc Problems

10

 

 

H. Disturbing a Chemical Equilibrium

5

 

 

I. Discussion Questions Chapter 13

5

 

 

Module Ten Total:

65

 

 

Part A: Equilibrium Constant Derivation 5 points

Derive the equilibrium constant expression

 

[C]c [D]d

Kc = ---------------

[A]a [B]b

 

from the rate expressions of the following reversible reaction:

 

aA + bB cC + dD

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part B: Equilibrium Constant Expressions 5 points

Write equilibrium constant expressions, Kc, for the following reactions they represent:

 

a. PCl3 (g) + Cl2 (g) PCl5 (g)

 

Kc =

 

b. 2 NOCl (g) 2 NO (g) + Cl2 (g)

 

Kc =

 

c. 4 HCl (g) + O2 (g) 2 H2O (g) + 2 Cl2 (g)

 

Kc =

 

 

d. CS2 (g) + H2 (g) CH4 (g) + H2S (g)

 

Kc =

 

 

e. CaCO3 (s) CaO (s) + CO2 (g)

 

 

Kc =

 

f. NH3 (g) + H2O (l) NH4 1+(aq) + OH1- (aq)

 

Kc =

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part C: The Equilibrium Constant K & Expression 5 points

 

Write five statements which explain what the equilibrium constant expression represents:

 

a)

 

 

b)

 

 

c)

 

 

d)

 

 

e)

 

 

Write five useful statements about the equilibrium constant:

 

 

a)

 

 

 

 

b)

 

 

 

c)

 

 

 

d)

 

 

 

e)

 

 

 

 

 

Part D: Equilibrium Constant, K & The Reaction Quotient, Q 5 points

 

Make three generalizations concerning the composition of equilibrium mixtures:

 

a)

 

 

b)

 

 

c)

 

 

Determining a reaction quotient is useful for two reasons, state the reasons:

 

 

a)

 

 

 

 

b)

 

 

 

 

Demonstrate the Usefulness of the reaction Quotient:

The brown gas nitrogen dioxide, NO2, will exist in equilibrium with the colorless gas, N2O4, K = 170 at 298 K.

 

2 NO2 (g) N2O4 (g) K = 170

 

Suppose that, at a specific time, the concentration of NO2 is 0.015M, the concentration of N2O4 is 0.025M.

 

a)    Is the Quotient Q larger than, or smaller than, or equal to K?

 

 

 

 

 

 

 

 

b)   If the system is not a equilibrium, in which direction will the reaction proceed to achieve equilibrium?

 

 

 

 

 

 

 

 

 

 

Picture Interpretation:

 

The Reaction A2 + B2 <====> 2 AB has an equilibrium constant Kc = 4. The following pictures represent reaction mixtures that contain A2 molecules (red), B2 molecules (blue) and AB molecules:

 

a) Which reaction mixtures is at equilibrium?

 

 

 

b) For the reaction mixtures that are not at equilibrium, will the net reaction go in the forward or the reverse direction to react equilibrium?

 

 

 

 

 

 

 

 

Part E: Experimental Determination of Equilibrium Constants 5 points

 

Calculate the equilibrium constant at 25oC for the reaction:

2 NOCl(g) 2 NO (g) + Cl2

when 2.00 moles of NOCl were placed in a 1.00-L flask, and the concentration of NO after equilibrium was achieved was 0.66 moles/liter.

 

 

[ ]

[ ]

[ ]

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part E: Experimental determination of Equilibrium Constants 5 points

A solution is prepared by dissolving 0.050 mol of diiodocyclohexane, C6H10I2 in the solvent CCl4. The total solution is 1.00 Liter. When the reaction:

C6H10I2 C6H10 + I2

has come to equilibrium at 35oC. The concentration of the I2 is 0.035 M.

(a)What are the concentrations of C6H10I2 and C6H10 at equilibrium?

 

 

[ ]

[ ]

[ ]

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

(b) Calculate the K, the equilibrium constant.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part F. Calculation Equilibrium Concentrations from Initial Concentrations based on Kc 5 points

 

At 25oC, Kc=0.090 for the reaction:

 

H2O (g) + Cl2O (g) 2 HOCl (g)

Calculate the concentration of all species if 2.0 mole of pure H2O and 2.0 mole of pure Cl2O are placed in a 2.0 L flask and the system is allowed to come to equilibrium.

 

 

 

[ ]

[ ]

[ ]

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part F. Calculations based on Kc 5 points

 

The reaction

. N2 (g) + O2 (g) 2 NO (g)

contributes to air pollution whenever fuel is burned at high temperatures and high pressure in an automobile gasoline engine. At 1500 K, K= 1.0 x 10 -5. Suppose a sample of air has

[N2] = 0.80 M and [O2] = 0.20 M before any reaction occurs. Calculate the equilibrium concentrations of the reactants and the products after the mixtures reaches 1500 K?

 

 

 

[ ]

[ ]

[ ]

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part G: LaChateliers Principle 5 points

Consider the isomerism of butane with an equilibrium constant of Kc = 2.5.

CH3

|

CH3-CH2-CH2-CH3 (n-butane) CH3-CH-CH3 (isobutane)

 

The system is originally at equilibrium with [n-butane]=1.0 M and [isobutane]=2.5M.

(a) If 0.50 moles/liter of isobutane is suddenly added and the system shifts to a new equilibrium position, what is the equilibrium concentration of each gas?

 

 

[ ]

[ ]

Initial

 

 

Change

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Part G: LaChateliers Principle 5 points

Carbonyl bromide decomposes to carbon monoxide and bromine gas.

 

COBr2 (g) CO (g) + Br2 (g)

 

K is 0.190 at 73oC. Suppose you placed 0.500 moles of COBr2 in a 1.00-L flask and heated it to 73oC. After equilibrium had been achieved, you added an additional 3.00 mol of CO.

 

 

Calculate the equilibrium concentration of each component before the CO is added:

 

 

[ ]

[ ]

[ ]

Initial

 

 

 

Change

 

 

 

Equilibrium

 

 

 

 

 

 

 

 

 

 

 

How is the equilibrium mixture affected by adding more CO?

 

 

 

When equilibrium is reestablished, what are the new equilibrium concentrations of each component?

 

 

 

 

 

 

 

 

 

 

How has the addition of CO affected the concentration of COBr2 that decomposed?

 

 

Part H: LaChateliers Principle Questions 5 points

Based on the followinq Equations, use the choices to describe the equibrium shifts, if any, when the following conditions are changed:

a. shifts left b. shifts right c. No effect

 

4 HCL (g) + O2 (g) 2 H2O (g) + 2 CL2 (g)

 

_____1. 1 mole of Chlorine gas is injected after equilibrium is reached

 

_____2. Water is removed after equilibrium is reached

 

_____3. Additional Heat is applied to system after equilibrium is reached,

(the reaction is exothermic)

 

_____4. Nitrogen gas is injected into the vessel after equilibrium is reached

 

_____5. Additional Oxygen gas is injected after equilibrium is reached

 

_____6. Increasing the size of the vessle from 1 to 3 liters after eq is reached

 

PCL5 PCl3 + CL2

 

 

_____7. Chlorine gas is injected into the vessle

 

_____8. Additional Heat is added to the system after equilibrium is achieved

(the reaction is endothermic)

 

_____9. Nitrogen gas is injected into the vessle

 

_____10. The gases are compressed into a vessle half the original size

after equilibrium is achieved.

Part I: Discussion Questions 5 points

1. What is dynamic equilibrium?

 

 

 

 

2. What is true about the initial rate of the forward and reverse reactions in a system where only reactants are present?

 

 

 

 

 

  1. a. What is true about the rates of the forward and reverse reactions at equilibrium?

 

b. What happens to the value of K when the reaction is reversed?

 

c. What happens to the value of K when the temperature is changed for the reaction?

 

 

 

4. Your textbook introduces the concept of equilibrium by noting that no reaction goes fully to completion. What does this imply about the reverse reaction?

 

 

 

 

5. Discuss the relationship between the magnitude of the equilibrium constants as to whether the forward or the reverse reaction is favored.

 

 

 

 

6. What effect does adding a catalyst on the concentrations of the reactants and products after equilibrium is established.

 

 

 

7. What disturbances are possible for a system in equilibrium?

 

 

 

8. When is it reasonable to neglect the change in the concentration in the denominator of an equilibrium constant expression when solving for the equilibrium concentrations from the initial concentrations.. (When does 1.0 M x ~ 1.0