5 - 1ch110: ch110 chapter 7 chemical reactions chemical equations types of reactions...

5 - 1CH110:

CH110 Chapter 7Chemical Reactions

Chemical Equations

Types of Reactions

Oxidation-Reduction

Energy in Chemical Reactions

Reaction Rates

Omit: Moles (7.1; 7.2; 7.6; 7.7)

5 - 2CH110:

What is Chemistry?“The study of Matter and its Changes.”

Physical Changes =

Changes in a Physical Property

Chemical Changes =

Changes in a Chemical Property

Appearance: • melting, freezing, evaporation…• stretching, molding, cutting…

Chemical Composition:

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Change in the Chemical Composition

Burning of Magnesium

Chemical Changes

Rusting of Iron

Decomposing of wood

Souring of Milk

Examples:

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Chemical Reactions

• Color change

• Gas formed

• Solid precipitate formed

• Temperature Change

• Gives heat = exothermic

• Gets cold = endothermic

5 - 5CH110:

Mg + O2 MgO +

Energy

Chemical Reactions

Shows how the Chemical change occurs.Shows how the Chemical change occurs.

Reactants

C3H8 + O2 CO2 + H2O + Energy

Fe + O2 Fe2O3

ProductsProducts

5 - 6CH110:

Chemical equations

Chemist’s shorthand to describe a reaction.

•Reactants •Products

•The state of all substances

H2 + O2 H2O + E(g) (g) (g)

•Any conditions used in the reaction

heat

•Same # & type atoms on each side• Law of Conservation of Matter

2 2

(g) (l) (s) (aq)(g) (l) (s) (aq)

5 - 7CH110:

Balancing Equations

___W10 + ___B8 ___WB___W10 + ___B8 ___WB

•Reactants •Products

Making Hot dogs:How many packages wieners & buns to buy so none is left over.

4 5 40

5 - 11CH110:

NaPO

MgCl

Balancing Equations

Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl

•Reactants •Products

Step 1: Count atoms of each element on both sides of equation.

31412

1 2831

5 - 12CH110:

NaPO

MgCl

Balancing Equations

Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl

•Reactants •Products31412

1 2831

- not balanced

- not balanced

Step 2: Determine which atoms are not balanced.

- not balanced

- not balanced

- not balanced

5 - 13CH110:

NaPO

MgCl

Balancing Equations

Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl

•Reactants •Products31412

1 2831

- not balanced

- not balanced

- not balanced

- not balanced

- not balanced

Step 3: Balance elements with #’s in front of formulas until all balanced.

(Never change the formulas!)

5 - 14CH110:

Hints:• Start with a metal in a complex

compound, or an element that only appears in one formula. (ie Mg here)

NaPO

MgCl

Balancing Equations

Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl Na3PO4 + MgCl2 Mg3(PO4)2 + NaCl

•Reactants •Products31412

1 2831

- not balanced

- not balanced

- not balanced

- not balanced

- not balanced66

66

63

33

22

66

1

88

2

66

5 - 15CH110:

Hints:• Start with an element that only appears

in one formula on both sides of the equation.

• Leave oxygen until last.

Balancing Equations

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

•Reactants •ProductsC

H

O

5 - 16CH110:

Balancing Equations

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

C

H

O

C

H

O

•Reactants •Products

Step 1: Count atoms of each element on both sides of equation.

2

6

2

2

6

2

1

2

3

1

2

3

5 - 17CH110:

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

Balancing Equations

•Reactants •Products

2

6

2

2

6

2

1

2

3

1

2

3

Step 2: Determine which atoms are not balanced.

- not balanced

- not balanced

- not balancedC

H

O

C

H

O

5 - 18CH110:

2

6

2

2

6

2

- not balanced

- not balanced

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

22

Balancing Equations

•Reactants •Products

1

2

3

1

2

3

- not balanced

Step 3: Balance one element at a time with coefficients in front of formulas until all balanced.

(Never change the formula!)

2

55

3

66

77

3.5

77

C

H

O

C

H

O

5 - 19CH110:

C

H

O

C

H

O

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

22

Balancing Equations

•Reactants •Products

2

6

2

2

6

2

1

2

3

1

2

3

2

55

3

66

77

3.5

77

Can’t have 3.5 O2 , so multiply equation by 2!

5 - 20CH110:

3.5C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

22

Balancing Equations

C

H

O

C

H

O

•Reactants •Products

2

6

2

2

6

2

1

2

3

1

2

3

4

55

6

66

77

7

77

Can’t have 3.5 O2 , so multiply equation by 2!

2

44 44

1212 1212

1414 1414

5 - 21CH110:

Types of Chemical Reactions

Complete:C3H8 + 5O2 3CO2 + 4H2O

Combustion

Incomplete:2C3H8 + 7O2 6CO + 8H2O

C3H8 + 2O2 3C + 4H2O

5 - 22CH110:

Types of Chemical Reactions

Combination

Decomposition

Single Replacement: Substitution

Double Replacement: Metathesis

A + BX B + AX

A + B C

C A + B

AX + BY BX + AY

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Combination Reactions

Rusting of Iron

4 Fe + 3 O2 2 Fe2O3

Formation of Acid Rain

SO3 + H2O H2SO4

2H2 + O2 2H2O

Exposion of Hydrogen Balloon

A + B C A + B C

Types of Chemical Reactions

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Decomposition Reactions

Heating Egg Shells

CaCO3 CaO + CO2

2 H2O2 2 H2O + O2

Blood with peroxide

C A + B

Types of Chemical Reactions

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Single Replacement Reactions

Iron Deposits on an Aluminum Pan

Al + FeCl3 Fe + AlCl3

A + BX B + AX

Types of Chemical Reactions

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Activity series of metalspotassiumsodium

potassiumsodium

calciumcalcium

magnesiumaluminum

zincchromium

magnesiumaluminum

zincchromium

ironnickel

tinlead

ironnickel

tinlead

coppersilver

platinumgold

coppersilver

platinumgold

Hydrogen

Al + Fe+3 Fe + Al+3

Fe + H+ Fe+3 + H2

incr

easi

ng

rea

ctiv

ity

Element give e’s to ion

lower on list

Element give e’s to ion

lower on list

5 - 27CH110:

Double Replacement Reaction

BaCl2(aq) + Na2SO4(aq) BaSO4(s) + 2NaCl(aq)

AX + BY BX + AY AX + BY BX + AY

Ba+2 Cl-1

Na+1 SO4-2

Insoluble PrecipitateFormed

Types of Chemical Reactions

5 - 28CH110:

Predict the products:

AgNO3(aq) + MgCl2(aq)

Ag+ NO3

-

Mg+2 Cl-

AgCl(s)

Double Replacement ReactionAX + BY BX + AY AX + BY BX + AY

Write correct formulas then balance as needed

2 2 + Mg(NO3)2(aq)

5 - 29CH110:

Oxidation and reductionREDOX

Where reactants exchange electrons -

Examples:

•All types of batteries

alkaline, NiCad, car batteries•Rusting and corrosion•Metabolism•Antioxidants (Vit C, E prevent oxidation)

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Oxidation and ReductionREDOXWhere reactants exchange electrons -

LEO the lion says GER LEO the lion says GER

Reduction = Gaining electrons GER: Gain Electrons Reduction

Oxidation = Losing electronsLEO: Lose Electrons Oxidation

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Oxidation and ReductionReduction =

GERGain e-s so gets more -

Oxidation = LEO

Lose e-s so gets more +

0+1+2+3+4

-1-2-3

-4

Fe3+ Fe2+

Na Na1+

5 - 32CH110:

Oxidation and Reduction

2 Na(s) + Cl2 (g) 2 NaCl2 Na(s) + Cl2 (g) 2 NaCl

1-1+

1. Assign Oxidation States:

0 0For simple ions,

Ox state = charge.

For element in natural form

Ox State = 0.

5 - 33CH110:

Oxidation and Reduction

2 Na(s) + Cl2 (g) 2 NaCl2 Na(s) + Cl2 (g) 2 NaCl

1-1+

2. Who’s loosing or gaining electrons?

0 0

Loses 1 e- = LEO

Gains 1 e-=GER

Na loses e- (LEO) Na gets oxidized

Cl gains e- (GER) Cl gets reduced

5 - 35CH110:

Oxidation and Reduction

2 Na(s) + Cl2 (g) 2 NaCl2 Na(s) + Cl2 (g) 2 NaCl

1-1+

Who’s loosing or gaining electrons?

0 0

• Na loses e- (LEO) so Na gets oxidized

• Na caused Cl to get reduced• Na is the Reducing agent

Loses 1 e- =LEO

Gains 1 e- =GER

5 - 36CH110:

Oxidation and Reduction

2 Na(s) + Cl2 (g) 2 NaCl2 Na(s) + Cl2 (g) 2 NaCl

1-1+

Who’s loosing or gaining electrons?

0 0

Loses 1 e- =LEO

Gains 1 e- =GER

• Cl gains e- (GER) so Cl gets reduced • Cl caused Na to get oxidized• Cl is the Oxidizing agent

5 - 39CH110:

H2OH2O

more stablemore stable

Energy in Chemical Reactions

Exothermic reactionExothermic reaction

-H= heat of reaction

En

erg

y

Rxn Progress

Reactants

Products

Eact= Activation Energy

(Gets hot)(Gets hot)

H2 + O2H2 + O2

2H2 + O22H2 + O2 2H2O + Energy2H2O + Energy

5 - 40CH110:

Exothermic ReactionsE

ner

gy

Rxn Progress

2Mg + O2 2MgO + Energy

2H2 + O2 2H2O + Energy

CH4 + 2O2 CO2 + 2H2O + 213 kcal

5 - 42CH110:

more stablemore stable

Energy in Chemical Reactions

Endothermic reactionEndothermic reaction

+H= heat of reactionEn

erg

y

Rxn Progress

Reactants

Products

Eact= Activation Energy

(Gets cold)(Gets cold)

5 - 44CH110:

En

erg

y

Rxn Progress

2H2(g) + O2(g) 2H2O + Energy2H2(g) + O2(g) 2H2O + Energy

Just because something has the potential to react doesn’t mean it will do so immediately.Just because something has the potential to react doesn’t mean it will do so immediately.

H2(g) + O2(g) may

stay together for

lifetime without

reacting to form

water.

H2(g) + O2(g) may

stay together for

lifetime without

reacting to form

water.

Reaction Rates

5 - 45CH110:

Oxidation: Paper burning Oxidation: Paper burning

Paper turning yellowPaper turning yellow

Oxidation: Nails rustingOxidation: Nails rusting

Reaction Rates

Fast:

Slow:

5 - 46CH110:

Rates of Reactions

Reaction rates can be affected by :Assuming reactant structure favor reaction

(polar vs. nonpolar) (vapor vs liq.)

1. temperature (hypothermia & metabolism)

2. concentration of reactants (medications)surface area (sugar cube vs crystals)

3. catalyst (H2O2 & blood)

5 - 47CH110:

They have to have enough E.

Reaction Rates

For reactants to make products:

•Molecules must collide

(solvents really help)

•They have to be aligned correctly.

(Parked cars don’t collide)

5 - 48CH110:

Reaction RatesFactors that increase reaction rate:

1. Higher Temperature:

Faster cars More collisions

More Energy More collisions

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Reaction Rates

Factors that increase reaction rate:2. Increased Concentration: More Reactants

More cars More collisions

8 blocks:34 surfaces

8 blocks:24 surfaces

More surface area More collisions

5 - 50CH110:

Reaction Rates

Factors that increase reaction rate:3. Adding a Catalyst:

Lower Eact More collisions

Uncatalysed reactionUncatalysed reaction

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Reaction Rates

Factors that increase reaction rate:3. Adding a Catalyst:

Lower Eact More collisions

Uncatalysed reactionUncatalysed reaction

Catalysed reactionCatalysed reaction

Lower activation energy

5 - 52CH110:

Alter the reaction mechanism but not change the products

Uncatalysed reactionUncatalysed reaction

Catalysed reactionCatalysed reaction

Lower activation energy

A catalyst will:

Enzymes are biological catalysts.Enzymes are biological catalysts.

Catalysts