CHEMICAL REACTIONS

Chapter 7

Changes

• PHYSICAL– Only affects the size,

shape and state.– Amount of

energy involved in each state varies.

• CHEMICAL– Atoms are rearranged.– Bonds broken– new substance

created– Energy released or

absorbed

Physical OR Chemical Reactions?

Lab: Conservation of MassPhysical or Chemical Change?

• A – Dissolving Salt and Water

• B – Melting Ice• C – Lead nitrate

mixed with sodium chloride OR sodium iodide

• D – copper and sulfur• E – water and alka-

seltzer

Lab: Conservation of MassPhysical or Chemical Change?

• A – Dissolving Salt and Water

• B – Melting Ice• C – Lead nitrate

mixed with sodium chloride OR sodium iodide

• D – copper and sulfur• E – water and alka-

seltzer

• Physical

• Physical

• Chemical

• Chemical

• Chemical

Chemical Reactions Rearrange atoms

REACTANTS PRODUCTS

C2H5OH + 3O2 2CO2 + 3H2O

New product atoms and old reactant atoms are not created or destroyed. Mass is always conserved.

Energy and Reactions

• Energy must be added to break bonds

• Energy– Heat– Electricity– Sound– light

• Forming bonds releases energy

Energy and Reactions

Energy and Reactions

Examples• Endothermic

– Photosynthesis– Dissolving most salts

into water (exceptions)– Decomposition

reactions        A –– > B + C

• Exothermic– Combustion of Methan

e (Natural Gas).

– Adding concentrated sulfuric acid to water

– Acid/Base reactions        Dissolving a strong acid or strong base

Diatomic Molecules• Most elemental gases do not exist as single atoms

• H2

• N2

• F2

• O2

• I2

• Cl2• Br2

7.2 Chemical Reactions AreRepresented by ChemicalEquations

7.2 Chemical Reactions AreRepresented by ChemicalEquations

Chemical EquationChemical Equation

A representation in which reactants are written before an arrow and

products are written after the arrow.

A representation in which reactants are written before an arrow and

products are written after the arrow.

ReactantsReactants ProductsProducts

ReactantsReactants

Substances that are about to chemically react.

Substances that are about to chemically react.

ProductsProducts

Substances that are formed from a chemical reaction.

Substances that are formed from a chemical reaction.

AnimationAnimation

“CO2flask.mov”“CO2flask.mov”

ReactantsReactants

Carbon,CCarbon,C

ReactantsReactants

Carbon,CCarbon,COxygen, O2Oxygen, O2

ReactantsReactants

Chemical reactionChemical reaction

ProductsProducts

Carbon Dioxide, CO2Carbon Dioxide, CO2

ProductsProducts

CoefficientsCoefficients

Integers used to indicate the ratio by which

reactants react and products form.

Integers used to indicate the ratio by which

reactants react and products form.

ReactantsReactants ProductsProducts

H2H2 O2

O2 H2OH2O++

ReactantsReactants ProductsProducts

H2H2 O2

O2 H2OH2O++22

ReactantsReactants ProductsProducts

H2H2 O2

O2 H2OH2O++22 11

ReactantsReactants ProductsProducts

H2H2 O2

O2 H2OH2O++22 11 22

ReactantsReactants ProductsProducts

H2H2 O2

O2 H2OH2O++22 22

ReactantsReactants ProductsProducts

H2H2 O2

O2 H2OH2O++22 22(g)(g) (g)(g) (g)(g)

Balancing Chemical Equations

Balancing Chemical Equations

Balancing GuidelinesBalancing Guidelines

1)Balance one element at a time.1)Balance one element at a time.

2) If you incidentally unbalance an element leave it alone.2) If you incidentally unbalance an element leave it alone.

3) Make successive passes.3) Make successive passes.

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al2O3Al2O3

CC CO2CO2++ AlAl ++

(not balanced)(not balanced)

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al Al

OOOC Al C OO

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al2O3Al2O3

CC CO2CO2++ AlAl ++22

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al Al

OOOC

Al

C OO

22

Al

Al2O3Al2O3

CC CO2CO2++ AlAl ++22

Al2O3Al2O3

CC CO2CO2++ AlAl ++22 3322

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al Al

OOO C

Al

C OO

22

Al

3322

C OO

C OOAl Al

OOO

Al2O3Al2O3

CC CO2CO2++ AlAl ++22 3322

Al2O3Al2O3

CC CO2CO2++ AlAl ++22 3322 33

Al2O3Al2O3

CC CO2CO2++ AlAl ++

Al Al

OOO C

Al

C OO

22

Al

3322

C OO

C OOAl Al

OOO

33

C

C

Al2O3Al2O3

CC CO2CO2++ AlAl ++44 3322 33

BalancedBalanced

Al Al

OOO C

Al

C OO

Al

C OO

C OOAl Al

OOO

C

C

Al

Al

Al2O3Al2O3

CC CO2CO2++ AlAl ++44 3322 33

BalancedBalanced

Na2SO3Na2SO3 S8

S8++

not balancednot balanced

Na2S2O3Na2S2O3

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

11 11

Na2SO3Na2SO3 S1

S1++ Na2S2O3Na2S2O3

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

11 11

88Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

11

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

SS SS

SS

SS

SS

SS

SS SS

8811

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

SS SS

SS

SS

SS

SS

SS SS

8811

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

SS SS

SS

SS

SS

SS

SS SS

8811

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

SS SS

SS

SS

SS

SS

SS SS

8811

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

8811

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

8811

11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

8811

88 11 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

88 88

8811

88 xx

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

88 88

8811

88 xx == 11

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

88 8811

Na2SO3Na2SO3 S8

S8++ Na2S2O3Na2S2O3

BalancedBalanced

88 8811

7.1 Chemical Reactions AreRepresented by ChemicalEquations

7.1 Chemical Reactions AreRepresented by ChemicalEquations

7.2 Chemists Use RelativeMasses to Count Atomsand Molecules

7.2 Chemists Use RelativeMasses to Count Atomsand Molecules

TYPES OF REACTIONS

Chapter 7

Types of Reaction• 1. Addition Reactions (aka synthesis)

A + B AB 2 or more substances combine to form a

new compound. small molecules join to form chains -

polymerization

Fe + O2 Fe2O3

Types of Reactions

• 2. Decomposition Reactions

AB A + B compounds are broken apart into

smaller substances

Example: Electrolysis of water

2 H2O 2 H2 + O2

Types of Reactions

• Single – Displacement Reaction

–AX + B BX + A

One element replaces a similar element in a compound

Aka Single – Replacement Reaction

Types of Reactions• Double – Displacement Reaction

–AB + CD AD + CB Aka double –replacement reactions Ions from 2 compounds in solution exchange

places to produce 2 new compounds.One of the compounds is usually …

A precipitateA gas that bubbles offA molecular compound like water

Types of Reactions

• Combustion Reactions–These use O2 as a reactant

–One product contains O and the other usually H2O

Carbon cpd. + O2 CO2 + H2O

___________________________________________________________________________________________________________________

Types of Reactions• Combustion Reactions

– These use O2 as a reactant

– One product contains O , usually H2O____________________________________________________________________________________________________________________________

Importance of Good Air Supply

2CH4 + 4O2 2CO2 + 4H2O

2CH4 + 3O2 2CO + 4H2O

2CH4 + 2O2 2C + 4H2O

Chapter 7.1 Energy in Reactions

Examples• Endothermic

– Melting of ice– evaporation of water– boiling of water. – Photosynthesis– Dissolving most salts

into water (exceptions)– Decomposition

reactions        AB –– > A + B

• Exothermic– Combustion of Methan

e (Natural Gas).

– Adding concentrated sulfuric acid to water

– Acid/Base reactions        Dissolving a strong acid or strong base

Other Terms - refers to the ease in which the reactions occurs

• Exergonic– Most cases:

are exothermic

– Bioluminescence– Respiration

• Endergonic– Most cases: are

endothermic

– Photosynthesis

Endothermic Reaction (ex. Photosynthesis) – takes in energy- cold pack

Exothermic Reactions (ex. Cell Respiration) – gives off energy– hot pack

Plus more balancing reactions to show conservation of mass and energy

__Cu+__O2__CuO __Cu+__S__CuS

H2O 2H2 + O2

CuCl2 + Zn ZnCl2 + Cu

HCl + NaOH HOH + NaClPbNO3 + KI PbI + KNO3

PbNO3+NaClPbCl +NaNO34CH3 + 7O2 4CO2 + 6H2O

            

860 × 691 - fphoto.photoshelter.com

            

605 × 500 - fphoto.com

2Cu+O22CuO or Cu+SCuS

__H2O __H2 + __O2

CuCl2 + Zn ZnCl2 + Cu

HCl + NaOH HOH + NaClPbNO3 + KI PbI + KNO3

PbNO3+NaClPbCl +NaNO34CH3 + 7O2 4CO2 + 6H2O

            

448 × 420 - witcombe.sbc.edu

2Cu+O22CuO or Cu+SCuS

2H2O 2H2 + O2

__CuCl2 + __Zn __ZnCl2 + __Cu

HCl + NaOH HOH + NaClPbNO3 + KI PbI + KNO3

PbNO3+NaClPbCl +NaNO34CH3 + 7O2 4CO2 + 6H2O

2Cu+O22CuO or Cu+SCuS

2H2O 2H2 + O2

CuCl2 + Zn ZnCl2 + Cu

__HCl + __NaOH __HOH + __NaCl__PbNO3 + __KI __PbI + __KNO3

__PbNO3+__NaCl__PbCl +__NaNO3

4CH3 + 7O2 4CO2 + 6H2O

2Cu+O22CuO or Cu+SCuS

2H2O 2H2 + O2

CuCl2 + Zn ZnCl2 + Cu

HCl + NaOH HOH + NaClPbNO3 + KI PbI + KNO3

PbNO3+NaClPbCl +NaNO3__CH4 + __O2 __CO2 + __H2O

Examples• Endothermic

– Melting of ice– evaporation of water– boiling of water. – Photosynthesis– Dissolving most salts

into water (exceptions)– Decomposition

reactions        A –– > B + C

• Exothermic– Combustion of

Methane (Natural Gas).

– Adding concentrated sulfuric acid to water

– Acid/Base reactions        Dissolving a strong acid or strong base