Reaction Rates and Equilibrium

(11 Days)


Tentative Dates

Topic(s)

Reading Assignments . . . Selected Sections in Chapters

Homework

5/13

A Study of Reaction Rates Lab Collision Theory, pp. 533 - 536 Supplemental Problems 1 - 7

5/14

A Study of Reaction Rates Lab--Data Processing & Collision Theory   Write-Up 1 (Graphs)

5/15

Reaction Mechanisms
Activation Energyy		 Reaction Mechanism & Activation Energy Reading Write-Up II (Finish Write Up)

5/16

Potential Energy Diagrams
Catalysts		 Factors Affecting Reaction Rates, pp 536 - 538
Catalyst Reading		 Supplemental Problems 8 - 16

5/19

Reversible Reactions . . . Equililbrium Reversible Reactions, pp. 539 - 541 Supplemental Problems 17 - 25

5/20

Le Chatelier's Principle Factors Affecting Equilibrium, pp. 541 - 544 Pre-Lab: Concentration and Temperature Effects on Equilibrium

5/21

Conc. and Temp. Effects on Equilibrium Lab Pre-Lab: Concentration and Temperature Effects on Equilibrium Write Up: Concentration and Temperature Effects on Equilibrium

5/22

Concentrations on Equilibria Computer Simulation Write Up: Concentration and Temperature Effects on Equilibrium Supplemental Problems 26 - 32

5/23

Equilibrium Constant Equilibrium Constants, pp. 545 - 548
Determining Whether A Reaction Will Occur, pp. 549 - 554		 Practice Problems 11, 12, p. 547
Concept Practice 48, 49, 50, p. 572
Concept Mastery 71, 72, 74, p. 573

5/27

Factors that Determine Equilibria and Review Determining Whether A Reaction Will Occur, pp. 549 - 554
Concept Summary 19.1, 19.2, 19.3		 Supplemmental Problems 33, 34
Study!!

5/28

Reaction Rates and Equilibria Test Pre-Lab: Acid/Base Titration Lab Pre-Lab: Acid/Base Titration Lab

Labs: A Study of Reaction Rates, Concentration and Temperature Effects on Equilibrium

Supplemental Problems:

1) Pick the member of each pair having the greater reaction rate. Assume similar conditions within each pair.

a) evaporation of gasoline or evaporation of water
b) fresh apples or bananas ripening in a grocery store
c) iron rusting or copper tarnishing
d) solid wax or paper burning

2) Use the idea that chemical reactions occur when particles collide to explain why an increase in the concentration of a reactant may cause an increase in the rate of a reaction.

3) The rate of a gaseous reaction may increase if the total pressure is increased. State three methods by which the pressure of a gaseous reaction might be increased.

4) If you tried to set a telephone directory book on fire with a match, you would not likely be successful. How would you have to modify the directory in order to light it with a match and have it burn? Explain your answer using collision theory.

5) The diagram at right shows the energy distribution of a substance at two different temperatures.

 

a) Which temperature is higher, T1 or T2?

b) Which temperature has the greater number of collisions with E, the energy needed to create a successful reaction?

c) How does this diagram explain why higher temperatures lead to faster reactions?

 

6) Consider two gases, A and B, in a container at room temperature. What effect will the following changes have on the rate of the reaction between these gases?

(a) The pressure is doubled (volume halved).
(b) The number of molecules of gas A is doubled.
(c) The temperature is decreased at constant volume.

7) In an important industrial process for producing ammonia (the Haber process), the overall reaction is

N2 (g) + 3 H2 (g) 2 NH3 (g) + 24,000 calories

A yield of approximately 98% can be obtained at 200o C and 1000 atmospheres of pressure.

(a) Is this reaction exothermic or endothermic?

(b) Suggest a reason for the fact that this reaction is generally carried out at a temperature of 500 o C and 350 atmospheres in spite of the fact that the yield under these conditions is only about 30 %.

(c) What is the heat of reaction in kilocalories per mole of NH3(g)?

(d) How many grams of hydrogen must react to form 1.6 moles of ammonia?

8) Do you think the equation

C2H4 (g) + 3 O2 (g) 2 CO2 (g) + 2 H2O (g)

represents the mechanism by which ethylene, C2H4, burns? (The reaction seems to imply that 1 ethylene molecule collides with 3 oxygen molecules.) Why?

9) A group of students is preparing a ten-page directory. The pages have been printed and are stacked in ten piles, page by page. The pages must be (1) assembled in order, (2) straightened, and (3) stapled in sets. If three students work together, each performing a different operation, which might be the rate-controlling step? What would be the effect on the overall rate if the first step were changed by ten helpers joining the individual assembling the sheets? What if these ten helpers joined the student working on the second step? The third step?

10) Hydrogen peroxide reacts with hydrogen ion and iodide ion according to this equation:

H+ + I- + H2O2 H2O + HOI

A possible mechanism for the reaction could be:

H+ + H2O2 H3O2 + (fast)
H3O2+ + I- H2O + HOI (slow)

(a) Show that the addition of these two equations gives the overall equation.
(b) Which is the rate-determining step?
(c) How would you expect the rate to be affected it the I- concentration is tripled?
(d) How would you expect the rate to be affected if the H+ concentration is tripled?

11) Use figure 19.4 on page 535 of your text to indicate which of the molecules is the activated complex. Use figure 19.5 to define activation energy.

12) Describe three situations at home or at school in which a minimum energy must be supplied before a "reaction" can take place.

13) The diagrams at right show how two graphs are related. The graph on the left shows the fraction of collisions possessing the activation energy of a chemical reaction. The graph on the right shows the energy of the reactants, the activated complex, and the products.

a) Which part on the left-hand graph shows molecules that don't collide with enough energy to produce a reaction? Which part shows collisions that do have enough energy to produce a reaction?

b) Indicate on the right-hand graph the energy of the reactants, the activated complex and the products.

14) An increase in temperature of 10 oC rarely doubles the kinetic energy of particles, and hence the number of collisions is not double. Yet, this temperature increase may be enough to double the rate of a reaction. Why is this true?

15) In a collision of particles what are the factors that determines whether a reaction will occur?

16) In the energy diagram of the reaction of 2 HI H2 + I2 found in your supplemental reading, why is kinetic energy decreasing as two HI go up the left side of the barrier and why is kinetic energy increasing as H2 and I2 go down the right side? Explain in terms of conservation of energy and also in terms of what is occurring to the various particles in relation to each other.

17) Phosphorus, P4, exposed to air burns spontaneously to give P4O10, the heat for this exothermic reaction is 712 kcal per mole of P4.

a) Draw a potential energy diagram for the net reaction explaining the critical parts of the curve.
b) How much heat is produced when 12.4 g of P4 burns?


18) Changing graphite in to diamonds takes less than 1 Kcal/mol of C (graphite), use your knowledge of reaction rates to account for the great difficulty found in the industrial process for accomplishing this?

19) Why does a burning match light a candle?

20) For the reaction CO + NO2 CO2 + NO, the activation energy for the forward reaction is known to be 32 kcal/mol.

(a) Calculatethe heat of reaction, using values from the heat of reaction table.

(b) Using the forward activation energy and the heat of reaction, calculate the activation energy for the reverse reaction.

(c) Draw the potential energy diagram for this system, indicating all three energy values.

21) Sketch a potential energy diagram which might represent an endothermic reaction. Label the parts of the curve representing activated complex, activation energy, and net energy absorbed.

22) Draw potential energy diagrams for two reactions that have the same heat of reaction, except that one reaction is fast and the other is slow.

23) Explain why a catalyst increases the rates of chemical reactions the same amount for both the forward and reverse reaction. Sketch a potential energy diagram to illustrate your explanation.

24) The reaction of S2O82- with I- is catalyzed by Cu2+ ions. A suggested mechanism involves these steps:

2 Cu 2+ + 2 I - 2 Cu+ + I2 (fast)
Cu + + S2O8 2- CuSO4 + + SO4 2- (slow)
Cu+ + CuSO4 + 2 Cu 2+ + SO4 2- (fast)


Add these equations to show that Cu 2+ is not consumed in the overall reaction.

25) The decomposition of hydrogen peroxide is catalyzed by iodide ions. The mechanism is thought to be as follows:

H2O2 + I - H2O + IO - (Slow)
IO - + H2O2 H2O + O2 + I - (Fast)

a) Identify the reaction intermediate and the catalyst. What's the difference?
b) Which reaction has the lowest activation energy?
c) Write the overall reaction.

26) Sugar is added to a cup of coffee until no more sugar will dissolve. Does addition of another spoonful of sugar increase the rate at which sugar molecules leave the crystal phase and enter the liquid phase? Will the sweetness of the liquid be increased by this addition? Explain

27). In the video, Dynamic Equilibrium, several experiments (sugar dissolving in tea, ice coolin tea, gold fish, gaseous bromine, liquid iodine, etc.) are described in which equilibrium is eventually reached. How do you recognize when equilibrium is reached in each of these three experiments? (You need a separate answer for each experiment.)

28) Is equilibrium established as a candle burns? Explain your answer.

29) The following chemical equation represents the reaction between hydrogen and chlorine to form hydrogen chloride:

H2 (g) + Cl2 (g) 2 HCl (g) + 44.0 Kcal

a) List four important pieces of information conveyed by this equation.
b) What are three important areas of interest concerning this reaction for which no information is indicated?
c) What is the maximum amount of HCl that could be produced from 10.0 g of H2?
e) 10.0 g of H2 could produce how much heat?

30) A well-studied reaction is the N2O4 (g) 2 NO2 (g) equilibrium. If 26.0 g of N2O4 decompose to form NO2, calculate:

a) the number of moles of NO2 formed.
b) the number of grams of NO2 formed.
c) the number of molecules of NO2 formed.
d) the number of liters of NO2 formed at standard temperature and pressure. (Remember that one mole of a gas = 22.4 L/mol at STP.)

31) Each of the following systems has come to equilibrium:

a) What will be the effect of an increase in pressure on each of the systems? (Increase in pressure is caused by a volume reduction.)
b) What will be the effect on the equilibrium concentration of each substance in the system when the listed reagent is added?

Reaction: Substance Added:
C2H6 (g) H2 (g) + C2H4 (g) H2 (g)
CO (g) + 1/2 O2 (g) CO2 (g) + heat Heat
Cu 2+ (aq) + 4 NH3 (aq) Cu (NH3)4 2+ (aq) CuSO4 (s) . . . a source of Cu 2+ ions
PbSO4 (s) + H + (aq) Pb 2+ (aq) + HSO4 - (aq) Pb(NO3)2 (s) . . . a source of Pb 2+ ions
Ag + (aq) + Cl - (aq) AgCl (s) NaCl (aq) . . . a source of Cl -1 ions

32) Given the equation for the reaction:

CO (g) + NO2 (g) CO2 + NO (g) + 54.1 Kcal

What happens in this system at equilibrium if

a) the temperature is increased?
b) the volume is decreased by a factor of ten?

33) For each of the following reactions, state (1) whether tendency toward minimum energy favors reactants or products and (2) whether tendency toward maximum randomness favors reactants or products.

(a) H2O (l) H2O (s) + 1.4 Kcal
(b) H2O (l) + 10 Kcal H2O (g)
(c) CaCO3 (s) + 43 Kcal CaO (s) + CO2 (g)
(d) I2 (s) + 1.6 Kcal I2 (in alcohol)
(e) 4 Fe (s) + 3 O2 (g) 2 Fe2O3 (s) + 400 Kcal

34) When a solid evaporates directly (without melting), the process is called sublimation. Sublmation of solid CO2 (dry ice) is a familiar example. Two other substances that sublime are FCN and ICN.

FCN (s) + 5.7 Kcal FCN (g)

ICN (s) + 14.2 Kcal ICN (g)

(a) In sublimation, does the tendency toward maximum randomness favor solid or gas?
(b) In sublimation, does the tendency toward minimum energy favor solid or gas?
(c) In view of your answer to (b), would you expect solid ICN to have a lower or higher vapor pressure than solid FCN at the same temperature.

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