Chapter 9 Chemical Equilibrium 9.1 Rates of Reactions

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Collision Theory of Reactions A chemical reaction occurs when • Collisions between molecules have sufficient energy to break the bonds in the reactants. • Molecules collide with the proper orientation. • Bonds between atoms of the reactants (N2 and O2) are broken, and new bonds (NO) form. Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Collision Theory of Reactions A chemical reaction does not take place if the • Collisions between molecules do not have sufficient energy to break the bonds in the reactants. • Molecules are not properly aligned. N2

O2

N2

O2

Activation Energy The activation energy • Is the minimum energy needed for a reaction to take place upon proper collision of reactants.

Reaction Rate and Temperature

Reaction rate

• Is the speed at which reactant is used up. • Is the speed at which product forms. • Increases when temperature rises because reacting molecules move faster, providing more colliding molecules with energy of activation.

Reaction Rate and Concentration Increasing the concentration of reactants • Increases the number of collisions. • Increases the reaction rate.

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Reaction Rate and Catalysts A catalyst • Speeds up the rate of a reaction. • Lowers the energy of activation. • Is not used up during the reaction.

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Factors That Increase Reaction Rate TABLE 9.1

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Learning Check State the effect of each on the rate of reaction as (I) increases, (D) decreases, or (N) no change. A. Increasing the temperature. B. Removing some of the reactants. C. Adding a catalyst. D. Placing the reaction flask in ice. E. Increasing the concentration of a reactant.

Solution State the effect of each on the rate of reaction as (I) increases, (D) decreases, or (N) no change. A. Increasing the temperature. (I) B. Removing some of the reactants. (D) C. Adding a catalyst. (I) D. Placing the reaction flask in ice. (D) E. Increasing the concentration of a reactant.

(I)

Learning Check Indicate the effect of each factor listed on the rate of the following reaction as (I) increases, (D) decreases, or (N) none: 2CO2 (g) 2CO(g) + O2(g) A. B. C. D.

Raising the temperature Removing O2 Adding a catalyst Lowering the temperature

Solution Indicate the effect of each factor listed on the rate of the following reaction as (I) increases, (D) decreases, or (N) none: 2CO2 (g) 2CO(g) + O2(g) A. Raising the temperature B. Adding O2 C. Adding a catalyst D. Lowering the temperature

(I) (D) (I) (D)

Chapter 9 Chemical Equilibrium 9.2 Chemical Equilibrium

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Reversible Reactions In a reversible reaction, there is both a forward and a reverse reaction. • Suppose SO2 and O2 are present initially. As they collide, the forward reaction begins. 2SO3 (g) 2SO2(g) + O2(g) • As SO3 molecules form, they also collide in the reverse reaction that forms reactants. The reversible reaction is written with a double arrow. forward

2SO2(g) + O2 (g)

reverse

2SO3(g)

Chemical Equilibrium At equilibrium • The rate of the forward reaction becomes equal to the rate of the reverse reaction. • The forward and reverse reactions continue at equal rates in both directions.

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Chemical Equilibrium When equilibrium is reached • There is no further change in the amounts of reactant and product.

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Equilibrium At equilibrium • The forward reaction of N2 and O2 forms NO. • The reverse reaction of 2NO forms N2 and O2. • The amounts of N2, O2, and NO remain constant. N2(g) + O2(g)

2NO(g)

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Learning Check Write the forward and reverse reactions for the following:

CH4(g) + 2H2S(g)

CS2(g) + 4H2(g)

Solution Write the forward and reverse reactions for the following: Forward: CH4(g) + 2H2S(g) CS2(g) + 4H2(g) Reverse: CS2(g) + 4H2(g) Or CH4(g) + 2H2S(g)

CH4(g) + 2H2S(g) CS2(g) + 4H2(g)

Learning Check Complete with 1. equal 2. not equal 3. forward 4. reverse 5. changes 6. does not change A. Reactants form products in the ________ reaction. B. At equilibrium, the reactant concentration _______. C. When products form reactants, it is the _______ reaction. D. At equilibrium, the rate of the forward reaction is ______ to the rate of the reverse reaction. E. If the forward reaction is faster than the reverse, the amount of products ________.

Solution A. Reactants proceed in the 3. forward reaction. B. At equilibrium, the reactant concentration 6. does not change . C. When products form reactants, it is the 4. reverse reaction. D. At equilibrium, the rate of the forward reaction is 1. equal to the rate of the reverse reaction. E. If the forward reaction is faster than the reverse, the amount of products 5. changes .

Chapter 5 Chemical Reactions and Quantities 5.3 Types of Reactions

Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings

Type of Reactions Chemical reactions can be classified as Combination reactions. Decomposition reactions. Single Replacement reactions. Double Replacement reactions.

Combination In a combination reaction, Two or more elements (or simple compounds) combine to form one product A

+

B

A

B

2Mg(s) + O2(g)

2MgO(s)

2Na(s) + Cl2(g)

2NaCl(s)

SO3(g) + H2O(l)

H2SO4(aq)

Formation of MgO

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Decomposition In a decomposition reaction, One substance splits into two or more simpler substances.

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2HgO(s)

2Hg(l) + O2(g)

2KClO3(s)

2KCl(s) + 3O2(g)

Decomposition of HgO

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Learning Check Classify the following reactions as 1) combination or 2) decomposition: ___A. H2(g) + Br2(g)

2HBr(l)

___B. Al2(CO3)3(s)

Al2O3(s) + 3CO2(g)

___C. 4Al(s) + 3C(s)

Al4C3(s)

Solution Classify the following reactions as 1) combination or 2) decomposition: 1 A. H2(g) + Br2(g) 2 B. Al2(CO3)3(s) 1 C. 4Al(s) + 3C(s)

2HBr(l) Al2O3(s) + 3CO2(g) Al4C3(s)

Single Replacement In a single replacement reaction, One element takes the place of a different element in a reacting compound.

Zn(s) + 2HCl(aq)

ZnCl2(aq) + H2(g)

Fe(s) + CuSO4(aq)

FeSO4(aq) + Cu(s)

Zn and HCl is a Single Replacement Reaction

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Double Replacement In a double replacement, Two elements in the reactants exchange places.

AgNO3(aq) + NaCl(aq)

AgCl(s) + NaNO3(aq)

ZnS(s)

ZnCl2(aq) + H2S(g)

+ 2HCl(aq)

Example of a Double Replacement

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Learning Check Classify the following reactions as 1) single replacement 2) double replacement A. 2Al(s) + 3H2SO4(aq)

Al2(SO4)3(s) + 3H2(g)

B. Na2SO4(aq) + 2AgNO3(aq)

Ag2SO4(s) + 2NaNO3(aq)

C. 3C(s) + Fe2O3(s)

2Fe(s) + 3CO(g)

Solution Classify the following reactions as 1) single replacement 2) double replacement 1 A. 2Al(s) + 3H2SO4(aq)

Al2(SO4)3(s) + 3H2(g)

2 B. Na2SO4(aq) + 2AgNO3(aq) Ag2SO4(s) + 2NaNO3(aq) 1 C. 3C(s) + Fe2O3(s)

2Fe(s) + 3CO(g)

Learning Check Identify each reaction as 1) combination

2) decomposition

3) single replacement 4) double replacement A. B. C. D. E.

3Ba(s) + N2(g) 2Ag(s) + H2S(aq) SiO2(s) + 4HF(aq) PbCl2(aq) + K2SO4(aq) K2CO3(s)

Ba3N2(s) Ag2S(s) + H2(g) SiF4(s) + 2H2O(l) 2KCl(aq) + PbSO4(s) K2O(aq) + CO2(g)

Solution 1 A. 3Ba(s) + N2(g) 3 B. 2Ag(s) + H2S(aq)

Ba3N2(s) Ag2S(s) + H2(g)

4 C. SiO2(s) + 4HF(aq) 2H2O(l)

SiF4(s) +

4 D. PbCl2(aq) + K2SO4(aq) PbSO4(s)

2KCl(aq) +

2 E. K2CO3(s)

K2O(aq) + CO2(g)