CHM 2046C Module10 Name:___________

Chapter 14 Module 10 Homework Packet

Module Ten: Chemical Equilibria Chapter 14

Possible

Answer

 

A. Equilibrium Constant Derivation from Reaction Rates Lecture

1

Answer

 

B. Writing Equilibrium Constant Expressions

1

Answer

 

C. Meaning of the Equilibrium Constant: K; Section 14.2 & Section 14.5 p699-701

1

Answer

 

D. Meaning of the Equilibrium Quotient: Q; Section 14.2 p691

1

Answer

 

E. Determination of Equilibrium Constants from Lab Data Section 14.7 p706-709

2

Answer

 

F. Determination of Equilibrium Conc from Kc Problems Section 14.8

2

Answer

 

G: La Chatelier's Principle Problems Lecture/Section 16.7 page 788

2

Answer

 

H. Disturbing a Chemical Equilibrium Section 14.6 pages 701-706

1

Answer

 

I. Discussion Questions Chapter 14

1

Answer

 

K. Key Terms - Chapter 14 & More about Equations & Eq Coefficients 14.6

1

Answer

 

Module Ten Total:

13

 

 

Part A: Equilibrium Constant Derivation 1 point

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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reading Reference: Lecture and Section 14.1

Part B: Equilibrium Constant Expressions 1 point

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 =

 

Reading Reference: Sections 14.1 and 14.2
Example 14.1 and Example 14.4
Try Practice 14.2; 14.3 p693; 14.10; 14.11 p699

Try Review Problems 14.27-14.30 page 725

Part C: The Equilibrium Constant K & Expression 1 point

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)

 

 

 

 

Reading Reference: Sections 14.2 and 14.3: Changing Dilutions P693; Add Chemical Equations p694:

Relation of Kc to Kp page 696; Heterogeneous Equilibrium Section 14.4
Look at Example 14.2 p695; Example 14.4 p 698;

Try Practice14.6; 14.7 page 696; Practice 14.8; 14.9 p697 Practice 14.10; 14,11 p698

 

 

Part D: Equilibrium Constant, K & The Reaction Quotient, Q 1 point

 

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?

 

 

 

 

 

 

 

 

 

 

 

  1. 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:

 

FG13_05-01UN

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?

 

 

 

 

 

 

 

 

 

 

Reading Reference: Section 14.5
Try Practice Exercise 14.12 page 700

Try Review Problems 14.31-14.34 page 725

Part E: Experimental Determination of Equilibrium Constants 2 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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reading Reference: Section 14.7 page 708

Look at Example 14.6 page 708
Try Practice Exercise 14.16; 14.17; 14.18 page 709

Try Review Problems 14.57-14.62 page 727

 

Part E: Experimental determination of Equilibrium Constants

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.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reading Reference: Section 14.7 page 708

Look at Example 14.6 page 708
Try Practice Exercise 14.16; 14.17; 14.18 page 709

Try Review Problems 14.57-14.62 page 727

 

Part F. Calculation Equilibrium Concentrations from Initial Concentrations based on Kc 2 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

 

 

 

 

Rearrange equation into the quadratic equation:

 

ax2 + bx + c = 0

 

Then solve by using the quadratic Formula:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reading Reference: Section 14.8

Look at Example 14.7 page 710
Try Practice Exercise 14.19; 14.20; page 710

Look at Example 14.8; 14.9; 14.10 Using Kc and Initial Concentrations page 711-718
Try Practice Exercise 14.21; 14.22;14.23 page 715-718

Try Review Problems 14.63-14.82 page 727-728

 

Part F. Calculations based on Kc continued

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

 

 

 

 

You may use assumptions I this calculation, show and prove assumption

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reading Reference: Section 14.8

Look at Example 14.10 Using Kc and Initial Concentrations page 716-718
Try Practice Exercise 14.23; 14.24 page 718

Try Review Problems 14.63-14.82 page 727-728

 

 

Part G: LaChateliers Principle 2 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

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Reading Reference: None--Lecture

No Practice Problems

 

 

 

Part G: LaChateliers Principle continued

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 1 point

 

Based on the following Equations, use the choices to describe the equilibrium 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 vessel from 1 to 3 liters after eq is reached

 

PCL5 PCl3 + CL2

 

_____7. Chlorine gas is injected into the vessel

 

_____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 vessel half the original size

after equilibrium is achieved.

Reading Reference: Section 14.6
Look at Example14.5 page 705 Try Practice: 14.14;14.15 page 706
Review Problems: 14.53-14.56 pages 726-727

Part I: Discussion Questions 1 point

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?)

 

 

 

Also see review questions: #14.1-#14.26 pages 724-725

 

 

Part K: Vocabulary / More Equilibrium Shifts Chapter 14 (1 point)

 

__________________ 1. If all the reactants and the products are in the same phase (such as

gases), then the we say the system is in _______________equilibrium.

 

__________________ 2. If at least one of the reactants or one of the products is not in the same

phase, then we say the system is in __________________ equilibrium.

 

__________________ 3. The state where the concentrations of the reactants and the products

remain constant with time , it is said that the system has reached a state

of ___________equilibrium.

 

__________________ 4. The _______ _________ Q is obtained by by applying the law of mass

action using the initial concentrations of both the reactants and the

products instead of the equilibrium concentration so as to determine the

direction of the equilibrium shift.

 

___________________5. ____________ ________________ states that if a change is imposed

on a system in equilibrium , the position of the equilibrium will shift in
a direction that tends to reduce that change.

 

Predict the effect on each of the following changes to the system on the direction of equilibrium:

a.       Moves to the Right

b.      Moves to the Left

c.       Has no effect/does not move left or right

 

The combination of hydrogen gas and oxygen gas to give water vapor can be expressed by
2 H2 (g) + O2 (g) 2 H2O (g)

 

_________6. Water is removed as it is being generated

 

_________ 7. Additional H2 is added

 

_________ 8. The system is cooled (assuming the reaction is exothermic)

 

_________ 9. The container is made larger

 

_________10. Nitrogen gas (which does not react with neither reactants nor products) is injected

into the cylinder causing a change in the pressure, Volume of vessel remains the

same.