Equilibrium, Redox Reactions, Hydrocarbons, and Functional Groups Chapters 18, 20, 22, and 23 Jennie...
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Transcript of Equilibrium, Redox Reactions, Hydrocarbons, and Functional Groups Chapters 18, 20, 22, and 23 Jennie...
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