CHEMICAL REACTIONS

Chemistry Matter and Change Chapter 9

Chapte

r 9 B

ig Id

ea

Millions of chemical reactions in and around you transform reactants into products, resulting

in the absorption or release of energy.

REACTIONS AND EQUATIONS

Chemistry Matter and Change Chapter 9.1

9.1

Main

Idea

Chemical reactions are represented by balanced

chemical equations.

9.1

Obje

ctives

• Recognize evidence of chemical reactions• Represent chemical

reactions with equations• Balance chemical

equations

9.1

Revie

w V

oca

bula

ry a

nd

Conce

pts • Chemical change• Dalton’s atomic theory• Law of conservation of

mass

9.1

New

Voca

bula

ry a

nd

Conce

pts

• Chemical reaction• Reactant• Product• Chemical equation• Coefficient• (s), (l), (g), (aq)• •

Chemical reaction

• Process by which atoms are rearranged

Evidence of chemical reactions

• Temperature/energy change• Gas emitted (odor)• Precipitate forms• Color change• Change of substance(s)

Representing chemical reactions

• 4+1=2+3• Reactant + reactant product +

product• Need one or more reactants and one

or more products

Symbols you need to know

Symbol Meaning

+ Plus

Yields

Reversible reaction

(s) Solid

(l) Liquid

(g) Gas

(aq) Aqueous (in water)

χ represents something that is needed for the reaction, but not consumed in the reaction x

Three types of equations

• Word equations• Skeletal equations• Chemical equations

Types of equations

Skeletal • Indicates

identity (by molecular formulae) of substances involved

Chemical • Indicates

identity (by molecular formulae) and relative quantity of substances involved

Word• Indicates

identity of substances involved

Hydrogen + oxygen water

H2 + O2 H2O 2H2 + O2 2H2O

Balancing chemical equations

• Conservation of mass–What goes in, must come out–What comes out, must have gone in

Balancing equations:

1. Write out word equation2. Write out skeletal equation3. Balance each atom– MINOH (aka Tarzan method)• Metals, ions, nonmetals, oxygen, hydrogen

– Start with “rare” elements– Leave atoms in multiple places until last“Me know chemistry,” said Tarzan as he

climbed the stoichiom-eh-tree.

Sample 1

• Magnesium and bromine form magnesium bromide–Mg + Br2 MgBr2 (balanced)

• Magnesium and oxygen form magnesium oxide–Mg + O2 MgO (not balanced)

– 2Mg + O2 2MgO (balanced)

Sample 2

• Nitrogen and hydrogen form ammonia

• N2 + H2 NH3

• N2 + 3H2 2NH3

Sample 3

• Zn + HCl ZnCl2 + H2

• Na + H2O NaOH + H2

For you to practice

• Fe + O2 Fe2O3

• Fe2O3 + H2 Fe + H2O

• Sb + O2 Sb4O6

• Al + HCl AlCl3 + H2

• H2O + CO2 C6H12O6 + O2

More hints

• Keep polyatomic ions together if they appear on both sides of the equation

• Diatomics always exist in pairs

Can you…

• Recognize evidence of chemical reactions

• Represent chemical reactions with equations

• Balance chemical equations

CLASSIFYING CHEMICAL REACTIONS

Chapter 9.2

9.2

Main

Idea

There are five types of chemical reactions:

synthesis, decomposition, single replacement, double

replacement, and combustion

9.2

Obje

ctives

• Classify chemical reactions• Identify the

characteristics of different classes of chemical reactions

9.2

Revie

w V

oca

bula

ry a

nd

Conce

pts • Metal• Nonmetal• precipitate

9.2

New

Voca

bula

ry a

nd

Conce

pts

• Synthesis reaction• Combustion reaction• Decomposition reaction• Single-replacement

reaction• Double replacement

reaction

5 Types of chemical reactions

1. Synthesis2. Decomposition3. Combustion 4. Single replacement (displacement)5. Double replacement (displacement)

Synthesis

• E+EC• Two or more reactants form one

product• 2H2 + O2 2H2O

+

Decomposition

• CE+E• One reactant breaks down into two

or more products• 2Fe2O3 4Fe + 3O2

+

Single replacement

• C + E E + C• One element in a compound is

replaced by another element• Br2 + MgCl2 MgBr2 + Cl2

+ +

Double replacement

• C+CC+C• Elements in both compounds change

partners• Ca(OH)2+2HClCaCl2+2H2O

+ +

Combustion

• C + O2 CO2 + H2O

• A compound plus oxygen produces an oxide and water

• 2C2H6 + 7O2 4CO2 + 6H20

Summary of reaction types

Reaction Type Reactants Probably Products Generic Equation

Synthesis Two or more substances

One compound A+BAB

Decomposition One compound Two or more substances

ABA+B

Single replacement A metal and a compoundA nonmetal and a compound

A new metal and compoundA new nonmetal and a compound

A+BXAX+B

Double replacement A metal and a compound

A new compound and metal

AX+BYAY+BX

Combustion Compound and oxygen

An oxide A+O2AO

Predict the product(s)

• NaOH+HCl • CH4+O2

• LiCl+Br2

• Fe+O2

• H2O

Can you…

• Classify chemical reactions• Identify the characteristics of

different classes of chemical reactions

REACTIONS IN AQUEOUS SOLUTIONS

9.3

9.3

Main

Idea

Double replacement reactions occur between substances in aqueous solutions and produce precipitates, water, or

gases.

9.3

Obje

ctives

• Describe aqueous solutions• Write complete ionic and

net ionic equations for chemical reactions in aqueous solutions• Predict whether

reactions in aqueous solutions will produce a precipitate, water or a gas

9.3

Revie

w V

oca

bula

ry a

nd

Conce

pts

• Solution• Ionic formulae• Precipitate• Ion

9.3

New

Voca

bula

ry a

nd

Conce

pts

• Aqueous solution• Solute• Solvent• Complete ionic equation• Spectator ion• Net ionic equation

Aqueous solutions

• Solvent- water• Solute- other substance(s)– HCl(aq) is hydrochloric acid in water

Types of reactions in aqueous solutions

• Form Gas – Usually Double displacement

Types of reactions in aqueous solutions

• Form Precipitate– Usually double

replacement

• 2KI + Pb(NO3)2 2KNO3+PbI2

Lead iodide

Types of reactions in aqueous solutions

• Form Water – Acid/base reactions• Double displacement

– Also form a salt

HCl + NaOH NaCl+ HOH

Net Ionic Reactions

• Allow you to predict the products in a double replacement reaction

• HBr(aq)+NaOH(aq)H2O(l)+NaBr(aq)

• H+(aq) + Br-

(aq) + Na +

(aq) + OH-(aq) H2O(l) + Na+

(aq)+ Br-(aq)

• H+ + OH-

H2O

Writing Net Ionic Reactions

• Perchloric acid reacts with aqueous potassium carbonate forming potassium chlorate, carbon dioxide gas and water.

Step 1: figure out the chemical formulae and phase for all substances

• Perchloric acid: HClO4(aq)

• Potassium carbonate: K2CO3(aq)

• Water: H2O(l)

• Carbon dioxide: CO2(g)

• Potassium perchlorate: KClO4

Writing Net Ionic Reactions

• Perchloric acid reacts with aqueous potassium carbonate forming potassium chlorate, carbon dioxide gas and water.

Step 2: write the skeletal equation

HClO4(aq)+K2CO3(aq) H2O(l)+CO2(g)

+KClO4(aq)

Writing Net Ionic Reactions

• Perchloric acid reacts with aqueous potassium carbonate forming potassium chlorate, carbon dioxide gas and water.

Step 3: balance the equation

2HClO4(aq) + K2CO3(aq) H2O(l)

+CO2(g) + 2KClO4(aq)

Writing Net Ionic Reactions

• Perchloric acid reacts with aqueous potassium carbonate forming carbon dioxide gas and water.

Step 4: Write the complete ionic equation

2H+(aq) + 2ClO4

-(aq) + 2K+

(aq) + CO32-

(aq)

H2O(l) + CO2(g) + 2K+(aq) + 2ClO4

-(aq)

Writing Net Ionic Reactions

• Perchloric acid reacts with aqueous potassium carbonate forming carbon dioxide gas and water.

Step 5: Cross out balanced terms

2H+(aq) + 2ClO4

-(aq) + 2K+

(aq) + CO32-

(aq)

H2O(l) + CO2(g) + 2K+(aq) + 2ClO4

-(aq)

Writing Net Ionic Reactions

• Perchloric acid reacts with aqueous potassium carbonate forming carbon dioxide gas and water.

Step 6: write net ionic equation

2H+(aq) + CO3

2-(aq) H2O(l) +CO2(g)

Practice

• Sulfuric acid reacts with aqueous sodium cyanide, forming hydrogen cyanide gas and aqueous sodium sulfate– You can reduce coefficients if you’d like

2H+(aq) + 2CN-

(aq) 2HCN(g)

or

H+(aq) + CN-

(aq) HCN(g)

Can you…

• Describe aqueous solutions• Write complete ionic and net ionic

equations for chemical reactions in aqueous solutions

• Predict whether reactions in aqueous solutions will produce a precipitate, water or a gas