Chapter 3

Chemical Reactions

2

Chemical and Physical Properties• Chemical Changes

– rusting or oxidation– chemical reactions

• Physical Changes– changes of state– density, color, solubility, melting, boiling

– Extensive Properties: depend on quantity– Intensive Properties: do not depend on quantity

3

States of Matter• Changes from one state to

another: Physical Change•heating•cooling

4

Physical Change vs. Chemical Change

5

Physical Change vs. Chemical Change

6

Chemical Equations

Symbolic representation of a chemical reaction (chemical change) that shows:

1. -reactants on left side of reaction2. -products on right side of equation3. -relative amounts of each using coefficients

H2 + O2 H2O

for a reaction to occur molecules, atoms, ions must interact with one another in the appropriate orientation under the right conditions

7

Chemical Equations• Are an attempt to show on paper

what is happening at the molecular level

8

Chemical Equations

• Look at the information an equation provides:

• • reactants products

1 formula unit 3 molecules 2 atoms 3 moles (molecule/mole) (moles/f.u.) (moles/f.u.)

(molecules.f.u.)

the states of matter also listed

)(CO 3 + Fe(s)2 CO(g) 3 +(s) OFe 232 g

9

Chemical Equations

10

Chemical Equations• Law of Conservation of Matter

– Matter is neither created nor destroyed in a chemical reaction• -There is no detectable change in quantity of

matter in an ordinary chemical reaction• -Balanced chemical equations must always include

the same number of each kind of atom on both sides of the equation

OH 4 CO 3 O 5 HC 22283

Balancing equations is a skill acquired only with a lot of practice!!!

By working many problems

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Balancing Composition Reactions

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

Mg(s) + O2(g) MgO(s)

Al(s) + Br2(l) AlBr3(s)

12

Balancing Reactions On Your Own

P4(s) + O2(g) P4O10(s)

CO(g) + O2(g) CO2(g)

P4(s) + Cl2(g) PCl3(l)

SO2(g) + O2(g) SO3(g)

P4O6(g) + O2(g) P4O10(s)

13

Balancing Decomposition Reactions

N2O(g) N2(g) + O2(g)

H2O2(aq) H2O(l) + O2(g)

AgBr(s) Ag(s) + Br2(l)

NH4HCO3(s) NH3(g) + H2O(g) + CO2(g)

14

Balancing Displacement Reactions on Your Own

AgNO3(aq) + Cu(s) CuNO3(aq) + Ag(s)

Al(s) + H2SO4(aq) Al2(SO4)3(aq) + H2(g)

Cl2(g) + NaI(aq) I2(s) + NaCl(aq)

CaCl2(aq) + Na3PO4(aq) NaCl(aq) + Ca3(PO4)2(s)

Ca(OH)2(aq) + HNO3(aq) Ca(NO3)2(aq) + H2O(l)

Ca(NO3)2(aq) + K2CO3(aq) KNO3(aq) + CaCO3(s)

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Law of Conservation of Matter

Combustion reaction: the burning of a fuel in oxygen producing oxides or oxygen containing compounds– -NH3 burns in oxygen to form nitrogen

monoxide and water

OH 6 + NO 4 O 5 + NH 4

or

OH 3 + NO 2 O + NH 2

223

2225

3

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Law of Conservation of Matter

• C7H16 burns in oxygen to form carbon dioxide and water.

17

Solutionsa mixture of two or more substances dissolved in

anotherSolute: substance present in the smaller amount that is dissolved

by the solventSolvent: substance present in the larger amount that dissolves the

solute

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Properties of Aqueous Solutions

• Electrolytes – produce ions in solution and conduct

electricity

– Strong electrolytes • ionize or dissociate 100% in water

– NaCl(s)Na+(aq) + Cl-(aq)

– Weak electrolytes • ionize or dissociate much less than 100% in

water– HF(l) H+(aq) + F-(aq)

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Strong Electrolytesconduct electricity extremely well

in dilute aqueous solutions– -ionize in water 100%

Examples:1. HCl, HNO3, etc

• strong soluble acids2. NaOH, KOH, etc

• strong soluble bases3. NaCl, KBr, etc

• soluble ionic salts

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Strong Ionic Salts

3(aq)2(aq)

100% OHs23

-(aq)(aq)

100% OH(s)

NO 2Ca )Ca(NO

ClNaNaCl

2

2

21

Weak Electrolytes

conduct electricity poorly in aqueous solutions-ionize much less than 100% in water

Examples:1. CH3COOH, (COOH)2

• weak acids

2. NH3, Fe(OH)3 • weak bases

22

Properties of Aqueous Solutions

Nonelectrolytes solutes that do not conduct electricity in water – do not “ionize”

• Examples:• C2H5OH – ethanol• Sugars – glucose, sucrose, etc.

23

Aqueous Solution Conductivity

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Solubility

• maximum amount of solute that can dissolve in a given amount of solvent– -defined as the amount of solute that dissolves in

100 g solvent

• Unsaturated Solution: • contains less than the maximum amount that

dissolves• Saturated solution: • contains the maximum amount that dissolves• Supersaturated solution: • contains more than the maximum amount that

normally dissolves

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Solubility

Rules for determining solubility:• soluble (dissolves) vs. insoluble (does not

dissolve)

Figure 5.3 on page 179

OH- and O2-, except Ba2+

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Soluble Insoluble Exceptions1. Group IA and ammonium salts (Li+, Na+, K+, NH4

+)___________

2. Acetates, nitrates, chlorates, perchlorates (CH3COO-, NO3

-, ClO3-,

ClO4-)

___________

3. most chlorides, bromides, and iodides (Cl-, Br -, I-)

Salts formed with Ag+,

Hg2+, Pb2+

4. most fluorides (F-) Salts formed with Group IIA

5. most sulfates (SO42-) Salts formed with Group IIA

(Ca2+, Sr2+, Ba2+), Ag+, Hg2+, Pb2+

6. most carbonates, phosphates, sulfides (CO3

2-, PO4

3-, S2-)

Salts formed with Group IA and NH4

+ (rule #1)

7. most oxides (O2-) _______________________

8. most hydroxides (OH-) Salts formed with Group IA and Ca2+, Sr2+

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Solubility

28

Metathesis Reactions

two ionic aqueous solutions are mixed and the ions switch partners

AX + BY AY + BX

Metathesis reactions remove ions from solution in 3 ways:

1. form H2O – neutralization (acid-base reactions)2. form an insoluble solid (precipitation reactions)3. form a gas

• -Ion removal is the driving force of metathesis reactions

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Precipitation ReactionsThree representation:

1. 1. Molecular equation

2. 2. Total ionic equation

aq3saqaq3 NaNOAgClNaCl AgNO

Ag+(aq) + NO3-(aq) + Na+ (aq) + Cl-(aq)

AgCl(s) + Na+ (aq) + NO3-(aq)

3. Net ionic equation

Ag+(aq) + Cl-(aq) AgCl(s)

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Precipitation Reactions

• 1. Molecular equation

(s)3)aq(3aq)(32(aq)23 CaCO +KNO 2 COK + )Ca(NO

2.Total ionic reaction

s3-

aq3aq

-2aq3aq

-aq3

2aq

CaCO NO 2K 2

COK 2 NO 2 Ca

3. Net ionic reaction

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Arrhenius Acids

substances that generate H3O+ (H+) in aqueous solutions

-Strong acids ionize 100% in water

-aqaq

%100g

-aqaq3

%100g

Cl H HCl

Cl OH HCl

orwater

-

aq3aqOH

3

-aq3aq3

100%2 3

NO + H HNO

or

NO + OH OH HNO

2

(l)

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Substances that donate protons (H+)

• Strong Acids

• Formula Name1. HCl hydrochloric acid2. HBr hydrobromic acid3. HI hydroiodic acid4. HNO3 nitric acid5. H2SO4 sulfuric acid6. HClO3 chloric acid7. HClO4 perchloric acid

Bronsted-Lowry Acids

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aq3-aq3

7% 23 OH + COOCH OH COOHCH

aq-aq3

7%

3 H + COOCH COOHCH

Acids

•-Weak acids ionize <100% in water

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•Common Weak Acids

•Formula Name

1.HF hydrofluoric acid

2.CH3COOH acetic acid (vinegar)

3.HCN hydrocyanic acid

4.HNO2 nitrous acid

5.H2CO3 carbonic acid (soda water)

6.H3PO4 phosphoric acid

Acids

35

• Substance that produce OH- ions in aqueous solution (water)

– Strong bases ionize 100% in water

(aq)OH 2 + (aq)Ba Ba(OH)

(aq)OH + (aq)K KOH-+2

2

-+

Arrhenius Bases

• Weak bases are covalent compounds that ionize <100% in water

-(aq)aq4

100%

2g3 OH + NH OH + NH

(l)

C C

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Substances that accept protons (H+)

• Strong bases:1. LiOH, NaOH, KOH, RbOH, CsOH,

Ca(OH)2, Sr(OH)2

2. Notice that they are all hydroxides of IA and IIA metals

Bronsted-Lowry Bases

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Acid-Base (neutralization) Reactions

form water and salt (ionic compound)– acid + base salt + water

• 1. Molecular equation

)(2 (aq)(aq)(aq) OH + KBr KOH + HBr

2. Total ionic equation

)(2-aqaq

-aqaq

-aqaq OH + Br+KOH+K+Br+H

3. Net ionic equation

l

(l)

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Acid-Base (neutralization) Reactions

1. Molecular equation

)(2aq)(23(aq)3(aq)2 OH 2 + )Ca(NOHNO 2 + Ca(OH)

2. Total ionic equation

)(2-

aq32aq

-aq3aq

-aq

2aq OH 2 +NO 2+ CaNO 2+ H 2+OH 2+Ca

3. Net ionic equation

(l)

(l)

39

There are four acid-base reaction combinations

that are possible:

1. strong acids – strong bases2. weak acids – strong bases3. strong acids – weak bases4. weak acids – weak bases

Acids and Bases

40

• Polyprotic acids: •Have more than 1 hydrogen ion that it can

donate to a base

1 mol sulfuric acid reacts with 1 mol sodium hydroxideH2SO4(aq) + NaOH(aq) NaHSO4(aq) + H2O(l)

1 mol sulfuric acid reacts with 2 mols sodium hydroxide

H2SO4(aq) + 2NaOH(aq) Na2SO4(aq) + 2H2O(l)

Acids and Bases

41

Gas Forming Reactions

H2CO3 H2O(l) + CO2 (g)

H2SO3 H2O(l) + SO2 (g)

NH4OH NH3(g) + H2O(l)