Equilibrium, Redox Reactions, Hydrocarbons,

and Functional Groups

Chapters 18, 20, 22,

and 23

Jennie L. Borders

Chapter 18 – Reaction Rates and Equilibrium

A rate is a measure of the speed of any change that occurs within an interval of time.

In chemistry, the rate of chemical change or the reaction rate is usually expressed as the amount of reactant changing per unit of time.

Section 18.1 – Rate of Reaction According to collision theory, particles

can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy.

The minimum energy that colliding particles must have in order to react is called the activation energy.

Activation Energy

Transition State An activated complex is an unstable

arrangement of atoms that forms momentarily at the peak of the activation-energy barrier.

The activated complex is sometimes called the transition state.

Factors Affecting Reaction Rates

The rate of a chemical reaction depends upon temperature, concentration, particle size, and use of a catalyst.

Temperature Usually, raising the temperature speeds

up reactions. Increasing the temperature increases

both the frequency of collisions and the number of particles that have enough energy to slip over the activation-energy barrier.

Concentration The number of particles in a given

volume affects the rate at which reactions occur.

More particles increase the concentration which increase the number of collisions leading to a higher reaction rate.

Particle Size The surface area of a reactant affects

the reaction rate. The smaller the particle, the more

surface area. An increase in surface area increases

the amount of the reactant exposed for reaction.

Catalysts A catalyst increases the rate of reaction

without being used up during the reaction.

Catalysts permit the reaction to proceed along a lower energy path.

Catalyst vs. No Catalyst

catalyst

Catalysts Since a catalyst is not consumed during

a reaction, it does not appear as a reactant or a product.

Instead, the catalyst is written above the yield arrow.

Enzymes

Enzymes in your digestive tract act as catalysts for breaking down proteins.

It takes your body a few hours to digest proteins.

Without the enzymes, it would take many years for you to digest your food.

Section 18.1 Assessment

1. How is the rate of a chemical reaction expressed?

2. What are four factors that affect the rate of a chemical reaction?

3. Does every collision between reaction particles lead to products? Explain.

4. Why does refrigerated food stay fresh longer than room temperature food?

Section 18.2 - Equilibrium A reversible reaction is one in which the

conversion of reactants to products and the conversion of products to reactants occur simultaneously.

Equilibrium When the rates of the forward and

reverse reactions are equal, the reaction has reached chemical equilibrium.

At chemical equilibrium, no net change occurs in the actual amounts of the components of the system.

Position The relative concentrations of the

reactants and products at equilibrium constitute the equilibrium position of a reaction.

The equilibrium position indicates whether the reactants or products are favored in a reversible reaction.

Le Chatelier’s Principle Le Chatelier’s Principle states that if a

stress is applied to a system in equilibrium, the system changes in a way that relieves the stress.

Stresses that upset the equilibrium include changes in the concentration of reactants or products, change in temperature, or changes in pressure.

Concentration Changing the concentration of any

reactant or product at equilibrium disturbs the equilibrium.

The system adjusts to minimize the effects of the change by shifting the equilibrium.

Temperature Increasing the temperature causes the

equilibrium position to shift to the direction that absorbs heat.

Think of heat as a reactant or product in the reaction.

Pressure A change in pressure only affects

gaseous equilibria that have an unequal number of moles of reactants and products.

Sample Problem What effect do each of the following changes

have on the equilibrium position for this following reaction?

PCl5(g) + heat PCl3(g) + Cl2(g)

a. Addition of Cl2b. Increase in pressurec. Removal of heatd. Removal of PCl3 as it is formed

equilibrium shifts to the left

equilibrium shifts to the right

equilibrium shifts to the left

equilibrium shifts to the left

Equilibrium Constant The equilibrium constant (Keq) is the

ratio of the product concentration to reactant concentration at equilibrium, with each concentration raised to a power equal to the number of moles of that substance in the balanced chemical equation.

Equilibrium ConstantGeneric Reaction:

aA + bB cC + dD

Equilibrium Constant:

Keq = [C]c x [D]d

[A]a x [B]b

Equilibrium Constant Keq > 1, products favored at equilibrium Keq < 1, reactants favored at equilibrium

Sample Problem A liter of a gas mixture at equilibrium

contains 0.0045mol or N2O4 and 0.030mol of NO2. Calculate Keq.

N2O4(g) 2NO2(g)

Keq = [NO2]2 Keq = (0.030M)2 = 0.20 [N2O4] (0.0045M)

Practice Problem At equilibrium, a 1L flask contains 0.15

mol H2, 0.25 mol N2, and 0.10 mol NH3. Calculate Keq for the reaction.

N2 + 3H2 2NH3

Keq = [NH3]2 Keq = (0.10M)2 = 11.85 [N2][H2]3 (0.25)(0.15)3

Section 18.2 Assessment1. How do the amounts of reactants and

products change after a reaction has reached chemical equilibrium?

2. What are three stresses that can upset the equilibrium of a chemical system?

3. What does the value of the equilibrium constant tell you about the amounts of reactants and products present at equilibrium?

Section 18.2 Assessment4. How can a balanced chemical equation be used to write an equilibrium-constant expression?5. Can a pressure change shift the equilibrium position in every reversible reaction? Explain.6. Using the following equilibrium constants, determine which reactions would favor the products.

a. 1 x 102 b. 0.003 c. 3.5

Chapter 20 – Oxidation-Reduction Reactions

Oxidation-reduction reactions are also known as redox reactions.

Oxidation is the loss of electrons or the gain of oxygen.

Reduction is the gain of electrons or the loss of oxygen.

Section 20.1 - Oxidation vs. Reduction The way to remember the difference in

oxidation and reduction is OIL RIG.

O = oxidation I = is L = loss of electrons

R = reduction I = isG = gain of electrons

Oxidation-Reduction Reactions

Mg(s) + S(s) Mg+2S-2(s)

Mg has a 0 charge and changes to Mg+2, so it loses electrons and is oxidized.

S has a 0 charge and changes to S-2, so it gains electrons and is reduced.

Oxidizing and Reducing Agents The substance that loses electrons is

called the reducing agent. The substance that accepts electrons is

called the oxidizing agent. In other words, the substance that is

reduced is the oxidizing agent, and the substance that is oxidized is the reducing agent.

Sample ProblemDetermine what is oxidized and what is reduced. Identify the oxidizing agent and the reducing agent.

2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag(s)

2Ag+NO3-(aq) + Cu0

(s) Cu+2(NO3-)2(aq) + 2Ag0

(s)

Ag goes from +1 to 0, so it gains electrons. Cu goes from 0 to +2, so it loses electrons.

Ag is reduced and is the oxidizing agent.Cu is oxidized and is the reducing agent.

Practice ProblemDetermine which substance is oxidized and which is reduced. Identify the oxidizing agent and the reducing agent.

4Al(s) + 3O2(g) 2Al2O3(s)

4Al0(s) + 3O20

(g) 2Al2+3O3-2

(s)

Al goes from 0 to +3, so it loses electrons. O goes from 0 to -2, so it gains electrons.

Al is oxidized and is the reducing agent.O is reduced and is the oxidizing agent.

Section 20.1 Assessment1. Define oxidation and reduction in

terms of loss or gain of oxygen.2. Define oxidation and reduction in

terms of loss or gain of electrons.3. How do you identify the oxidizing

agent and the reducing agent in a redox reaction?

Section 20.1 Assessment4. Determine which substance is oxidized and which is reduced. Identify the oxidizing agent and reducing agent.

Mg(s) + Cu(NO3)2(aq) Mg(NO3)2(aq) + Cu(s)

Mg0(s) + Cu+2(NO3

-)2(aq) Mg+2(NO3-)2(aq) + Cu0

(s)

Mg goes from 0 to +2, so it loses electrons. Cu goes from +2 to 0, so it gains electrons.

Mg is oxidized and is the reducing agent.Cu is reduced and is the oxidizing agent.

Section 20.2 – Oxidation Numbers An oxidation number is a

positive or negative number assigned to an atom to indicate its degree of oxidation or reduction.

A bonded atom’s oxidation number is the charge that it would have if the electrons in the bonded were assigned to the atom of the more electronegative element.

Rules for Oxidation Numbers1. The oxidation number of a monatomic ion is

equal to its ionic charge.Ex: Br- = -1 Fe+3 = +3

2. The oxidation number for H is +1 except in metal hydrides where it is -1.

Ex: HCl, H = +1 NaH, H = -1

3. The oxidation number for oxygen is -2 except in peroxides where it is -1.Ex: MgO, O = -2 H2O2, O = -1

Rules for Oxidation Numbers4. The oxidation number of a nonbonded

element is 0.Ex: Ag = 0 N2 = 0

5. For a neutral compound, the sum of the oxidation numbers must equal 0.

Ex: NaCl = +1 and -1 equal 0. H2O = 2(+1) and -2 equal 0.

6. For a polyatomic ion, the sum of the oxidation numbers must equal the ionic charge of the ion.

Ex: CO3-2, O = -2, so C = +4

4 + (3 x -2) = -2

Oxidation Numbers

Sample ProblemWhat is the oxidation number of each element in Na2SO4?

Na2SO4 = Na2+SO4

-2 so Na is +1

SO4-2 = O is -2, so S has to be +6

Na=+1, O=-2, and S=+6

Practice Problems1. Assign the oxidation numbers for each

element in SO2.

2. Assign the oxidation number for each element in (NH4)2S.

SO2, O = -2, so S would be +4

O=-2 and S=+4

(NH4)2S = (NH4)2+S-2, so S = -2

NH4+, H = +1, so N would be -3

N=-3, H=+1, and S = -2

Oxidation Numbers In some redox reactions, it is necessary

to look at oxidation numbers instead of just using charges.

Sample ProblemIdentify which atoms are oxidized and which are reduced in the reaction.

2KNO3(s) 2KNO2(s) + O2(g)

+1 +5 -2 +1 +3 -2 0

2KNO3(s) 2KNO2(s) + O2(g)

Since N went from +5 to +3, it is reduced.Since O went from -2 to 0, it is oxidized.

Practice ProblemIdentify which atoms are oxidized and which are reduced in the reaction.2HNO3(aq) + 6HI(aq) 2NO(g) + 3I2(s) + 4H2O(l)

+1 +5 -2 +1 -1 +2 -2 0 +1 -2

2HNO3(aq) + 6HI(aq) 2NO(g) + 3I2(s) + 4H2O(l)

Since N goes form +5 to +2, it is reduced.Since I goes form -1 to 0, it is oxidized.

Section 20.2 Assessment1. What is the general rule for assigning

oxidation numbers?2. Identify which atoms are oxidized and

which are reduced.2Na(s) + Cl2(g) 2NaCl(s)

0 0 +1 -1

2Na(s) + Cl2(g) 2NaCl(s)

Since Na goes from 0 to +1, it is oxidized.Since Cl goes from 0 to -1, it is reduced.

Chapter 22 – Hydrocarbon Compounds

Compounds that contain carbon are classified as organic compounds.

The simplest organic compounds contain only carbon and hydrogen and are called hydrocarbons.

Section 22.1 - Hydrocarbons

Because carbon has four valence electrons, a carbon atom always forms four covalent bonds.

Alkanes An alkane is a hydrocarbon in which

there are only single covalent bonds. The carbon atoms in an alkane can be

arranged in a straight chain or in a chain that has branches.

Naming Alkanes The following chart shows the names for

straight-chain alkanes containing 1 to 10 carbons.

# Carbon Name MolecularFormula

1  Methane  CH4 

2  Ethane  C2H6 

3  Propane  C3H8 

4  Butane  C4H10 

5  Pentane  C5H12 

6  Hexane  C6H14 

7  Heptane  C7H16 

8  Octane  C8H18 

9  Nonane  C9H20 

10  Decane  C10H22 

Writing the Formulas for Hydrocarbons

Molecular Formula C6H14

Branched-Chain Alkanes An atom or group of atoms that can take

the place of a hydrogen atom on a parent hydrocarbon is called a substituent.

The longest continuous carbon chain of a branched-chain hydrocarbon is called the parent alkane.

Alkyl Group A hydrocarbon substituent is called an

alkyl group. Alkyl groups are named by removing the

–ane ending from the parent hydrocarbon and adding –yl.

Ex: methane = methyl ethane = ethyl

Naming Branched-Chain Alkanes

The IUPAC rules for naming branched-chain alkanes are based on the name of the longest continuous carbon chain.

Each alkyl substituent is named according to the length of the chain and numbered according to its position on the main chain.

IUPAC Rules1. The longest chain is the parent chain.2. Number the carbons in the parent

chain in order so that the groups attached to the chain will have the smallest numbers.

3. Add numbers to the names of the substituent groups to identify their positions.

IUPAC Rules4. Use prefixes to indicate the appearance of the

same group more than once in the structural formula.

5. List the names of the alkyl substituents in alphabetical order, but ignore any prefixes.

6. Use proper punctuation.Commas are used to separate numbers, and hyphens are used to separate numbers andwords.

Sample Problems

Name the following compound.

4-ethyl-2,3-dimethylheptane

1 2 3 4 5 6 77 6 5 4 3 2 1

Sample Problems Name the following compound.

6

5

43 2 1

2,3,4-trimethylhexane

Practice Problems1. Name the following compound.

4 3 2 5

6 1

7

4-ethyl-3,3,4-trimethylheptane

Practice Problems1. Name the following compound.

4 3

5 2

6 1

7

4,4-diethylheptane

Drawing a Structural Formula

1. Write the parent chain (the ending of the name).

2. Number the carbons.3. Attach the substituent groups.4. Add hydrogens as needed until all

carbons have 4 bonds.

Sample Problem1. Draw the structural formula for 2,2,4-trimethylpentane.

1st draw pentane (5 carbons).

C - C - C - C - C

CH3

ICH3

I

ICH3

2nd add a methyl (-CH3) group to the 2, 2, and 4.

3rd fill in H’s until each C has 4 bonds.

H3 H2 H H3

Practice Problem1. Draw the structural formula for 4-ethyl-2,3,4-trimethyloctane.

1st draw octane (8 carbons).

2nd add an ethyl (CH3CH2-) to 4 and a methyl (CH3-)to 2, 3, and 4.3rd add H’s until each C has 4 bonds.

C - C - C - C - C - C - C - C ICH3

ICH3

ICH3

CH2CH3

IH3 H H H2 H2 H2 H3

Section 22.1 Assessment1. Explain why carbon atoms form four

covalent bonds.2. Write the structural formula for the

following alkanes.a. propane b. pentane

3. Draw the structural formula for 2,2-dimethylbutane.

CH3

ICH3-C-CH2-CH3

I CH3

Section 22.2 – Unsaturated Hydrocarbons Organic molecules that contain the

maximum amount of hydrogen atoms per carbon atoms are called saturated compounds.

Compounds that contain double or triple bonds are called unsaturated compounds.

AlkaneR–CH2–CH2–

R

Alkene R–CH=CH–R

Alkyne R–C≡C–R

Alkenes Alkenes are hydrocarbons that contain

one or more carbon-carbon double covalent bonds.

When naming alkenes, find the longest chain that includes the double bond and change the ending of the alkane name to –ene. Ex: butane = butene

Naming Alkenes The carbons should be numbered so

that the double bonded carbons have the lowest number.

Any substituents should follow the rules that we have already covered.

Alkynes Hydrocarbons that contain one or more

carbon-carbon triple bonds are called alkynes.

Alkynes are named like alkenes, except that the alkane name ending changes to –yne. Ex: propane = propyne

Sample Problem Name the following compound.

1 2 3 4 5 6 77 6 5 4 3 2 1

3-methyl-2-heptene

Practice Problem Name the following compound.

CH3 ICH3-CH2-C C-CH-CH-CH2-CH3

I CH2CH3

1 2 3 4 5 6 7 8

5-ethyl-6-methyl-3-octyne

Section 22.2 Assessment Describe the bonding between atoms in

an alkene. What types of bonds are present in an

alkyne? What is the difference between

saturated and unsaturated hydrocarbons?

Chapter 23 – Functional Groups

The substituents of organic molecules often contain oxygen, nitrogen, sulfur, and/or phosphorus.

A functional group is a specific arrangement of atoms in an organic compound that is capable of characteristic chemical reactions.

Section 23.1 – Functional Groups

The symbol R represents any carbon chains or rings attached to the functional group.

Double bonds and triple bonds are also considered functional groups.

A halocarbon is a carbon containing compound with a halogen substituent.

Functional Groups

phenyl

Functional Groups

Section 23.1 Assessment1. What is a halocarbon?2. Identify the functional group in each

structure.a. CH3-OH

b. CH3-CH2-NH2

c. C - OH II O

d. CH3-CH2-CH2-Br

e. CH3-CH2-O-CH2-CH3