5 - 1GS105 CHGS105 Chapter 17 Chemical Reactions Chemical Changes Chemical Equations Types of...

5 - 1GS105

CHGS105 Chapter 17Chemical Reactions

Chemical Changes

Chemical Equations

Types of Reactions

Oxidation-Reduction

Moles

Energy in Chemical Reactions

Reaction Rates

5 - 2GS105

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:

5 - 3GS105

Change in the Chemical Composition

Burning of Magnesium

Chemical Changes

Rusting of Iron

Decomposing of wood

Souring of Milk

Examples:

5 - 4GS105

Chemical Reactions

• Color change

• Gas formed

• Solid precipitate formed

• Temperature Change

• Gives heat = exothermic

• Gets cold = endothermic

5 - 6GS105

Mg + O2 MgO +

Energy

Chemical Equations

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

Reactants

C3H8 + O2 CO2 + H2O + Energy

Fe + O2 Fe2O3

ProductsProducts

5 - 7GS105

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 - 8GS105

Law of Conservation of MatterQuestion:

5 - 9GS105

Law of Conservation of MatterSolution: Fe + O2 Fe2O3

5 - 10GS105

Law of Conservation of MatterQuestion:

5 - 11GS105

Law of Conservation of MatterSolution:

5 - 12GS105

Balancing Equations

___W10 + ___B8 ___WB___W10 + ___B8 ___WB


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

4 5 40

5 - 13GS105

Ca

H

Cl

Balancing Equations

Ca + HCl CaCl2 + H2 Ca + HCl CaCl2 + H2


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

1

1

1

1

2

2

5 - 14GS105

Balancing Equations


Ca

H

Cl

Ca

H

Cl


1

1

1

1

1

1

1

2

2

1

2

2

Step 2: Determine which atoms are not balanced.

- not balanced

- not balanced

5 - 15GS105

Balancing Equations



1

1

1

1

1

1

1

2

2

1

2

2

- not balanced

- not balanced

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

(Never change the formula!)

2

22

Ca

H

Cl

Ca

H

Cl

22

5 - 16GS105

NaPO

MgCl

Balancing Equations

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



31412

1 2831

5 - 17GS105

NaPO

MgCl

Balancing Equations


•Reactants •Products31412

1 2831

- not balanced

- not balanced


- not balanced

- not balanced

- not balanced

5 - 18GS105

NaPO

MgCl

Balancing Equations



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 - 19GS105

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



1 2831

- not balanced

- not balanced

- not balanced

- not balanced

- not balanced66

66

63

33

22

66

1

88

2

66

5 - 20GS105

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 - 21GS105

Balancing Equations

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

C

H

O

C

H

O



2

6

2

2

6

2

1

2

3

1

2

3

5 - 22GS105

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

Balancing Equations


2

6

2

2

6

2

1

2

3

1

2

3


- not balanced

- not balanced

- not balancedC

H

O

C

H

O

5 - 23GS105

2

6

2

2

6

2

- not balanced

- not balanced

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

22

Balancing Equations


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 - 24GS105

C

H

O

C

H

O

C2H6 + O2 CO2 + H2OC2H6 + O2 CO2 + H2O

22

Balancing Equations


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 - 25GS105

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

22

Balancing Equations

C

H

O

C

H

O


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 - 26GS105

___O2 ____O3

___Cr + ___O2 ____Cr2O3

___HNO2 ___HNO3 + ___NO + __ H2O

___N2H4O3 ___N2 + ___O2 + ___H2O

___N2O ____N2 + ____O2

___NO + ___O2 ____NO2

___CH4 + ___O2 --> CO2 + ____H2O

Balancing EquationsPractice:

5 - 27GS105

___O2 ____O3

___Cr + ___O2 ____Cr2O3

___HNO2 ___HNO3 + ___NO + __ H2O _

_N2H4O3 _ _N2 + _ _O2 + _ _H2O

___N2O ____N2 + ____O2

___NO + ___O2 ____NO2

___CH4 + ___O2 --> CO2 + ____H2O

Balancing EquationsSolutions:

3 2

34 2

3

2

2

4

2

2

2

2 2

2

5 - 28GS105

Types of Chemical Reactions

Complete:C3H8 + 5O2 3CO2 + 4H2O

Combustion

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

C3H8 + 2O2 3C + 4H2O

5 - 29GS105

Combination Reactions

Rusting of Iron

4 Fe + 3 O2 2 Fe2O3

2H2 + O2 2H2O

Exposion of Hydrogen BalloonA + B C A + B C

Decomposition Reactions

2 H2O2 2 H2O + O2

Blood with peroxide C A + B

5 - 30GS105

Single Replacement Reactions

Iron Deposits on an Aluminum Pan

Al + FeCl3 Fe + AlCl3

A + BX B + AX

Double Replacement Reaction

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

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

Insoluble PrecipitateFormed

5 - 31GS105

1 pair =

1 dozen =

1 mole =

1 pair =

1 dozen =

1 mole =

The Mole

1 mol eggs___

6.02 x 1023eggs

1 mol Au_______

6.02 x 1023 Au atoms

_____1 mole H2O_____

6.02 x 1023 H2O molecules

2

12

6.02 x 1023

602,000,000,000,000,000,000,000.

5 - 32GS105

1 car ___ 4 wheels

The Mole & Formulas

1 mol cars_

4 mol wheels1 doz cars4 doz wheels

1 mole H2O

2 mol H

1 mole H2O

1 mol O

5 - 33GS105

1 mole = MW in g’s The Mole & Molecular Mass

1 mol S_

32 g S

1 mol S_

32 g S

1 mole S = 32 g S1 mole S = 32 g S

32 g S

1 mol S

32 g S

1 mol S

1 mol C

12 g C

1 mol C

12 g C

1 mole C = 12 g C1 mole C = 12 g C

12 g C

1 mol C

12 g C

1 mol C

__32 g S _

6.02 x 1023 atoms S

__32 g S _

6.02 x 1023 atoms S

__12 g C _

6.02 x 1023 atoms C

__12 g C _

6.02 x 1023 atoms C

5 - 34GS105

5 - 37GS105

1 mol H2O =

18 g H2O

Mass to Mole Conversions

How many moles of water are in 36 g H2O?

What should the answer look like?

What is Unique to the problem?

36 g H2O

1

mol H2O2.0

1 mol H2O_

18.0 g H2O

18.0 g H2O

1 mol H2O

5 - 38GS105

1 mol H2O

18 g H2O

Mass to Mole Conversions

How many molecules of water are in 36 g H2O?

What should the answer look like?

What is Unique to the problem?

36 g H2O

1= molecules H2O

1.2 x 1024

molecules H2O

1 mol H2O_

18.0 g H2O

1 mol H2O_

6.02x1023 molecules H2O

6.02x1023 molecules H2O _

1 mol H2O

5 - 41GS105

Ratios in Chemical Equations

C(s) + O2 (g) CO2(g)

1 mol C

1 mol O2

1 mol C 1 mol CO2

1 mol O2

1 mol CO2

12 gs of C + 32 gs of O2 44 g CO2

12 g C

32 g O2

12 g C 44 g CO2

32 g O2

44 g CO2

5 - 42GS105


C(s) + O2 (g) CO2(g)

1 mol C

1 mol O2

1 mol C 1 mol CO2

1 mol O2

1 mol CO2

How many gs of O2 are needed to

produce 11 g CO2?

12 g C

32 g O2

12 g C 44 g CO2

32 g O2

44 g CO2

5 - 43GS105

11 g CO2


32 g O2

44 g CO2

1 mol O2

1 mol CO2

• If it takes 32 g O2 to make 44 g CO2 then:

11 g CO2

= g O2 8

C(s) + O2 (g) CO2(g)

How many gs of O2 are needed to make 11 g CO2?

32 g O2

44 g CO2

X g O2

11 g CO2

= 32 g O2

44 g CO2

X g O2

11 g CO2

=

5 - 44GS105


32 g O2

44 g CO2

1 mol O2

1 mol CO2

• Identify any conversion factors.

•How should the answer look?

11 g CO2 = g O2

• What is unique to the problem?

8 32 g O2

44 g CO2

C(s) + O2 (g) CO2(g)


Factor conversion method:

5 - 45GS105


11 g CO2 = g O2 8 32 g O2

44 g CO2

C(s) + O2 (g) CO2(g)


? gs C + 8 gs O2 11 g CO2So: 3

5 gs C + 8 gs O2 13 g CO2 ?Then could :

NO! There is only enough O2 to make 11 g’s of CO2. We

would still make 11 g’s of CO2 but have 2 g’s of C left over

5 - 46GS105

Moles in Chemical Equations

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

2 mol Na

1 mol Cl2

2 mol Na 2 mol NaCl

1 mol Cl2

2 mol NaCl

How many gs of Cl2 are needed to produce

2.5 mol NaCl?

46 g Na

71 g Cl2

46 g Na 58.5 g NaCl

71 g Cl2

58.5 g NaCl

5 - 47GS105

Moles in Chemical Equations2 Na(s) + Cl2 (g) 2 NaCl

1 mol Cl2

70.9 g Cl2

1 mol Cl2

2 mol NaCl

How many gs of Cl2 are needed to produce 2.5 mol NaCl?

= 89 gCl2

• How many moles of Cl2 are needed? X mol Cl2

2.5 mol NaCl

1 mol Cl2

2 mol NaCl= • How many grams of Cl2 are needed?

mol Cl2

X g Cl2

=

1 mol Cl2

71 g Cl2

1.25

1.25

5 - 48GS105

Moles in Chemical Equations2 Na(s) + Cl2 (g) 2 NaCl

1 mol Cl2

70.9 g Cl2

1 mol Cl2

2 mol NaCl

How many gs of Cl2 are needed to produce 2.5 mol NaCl?

• Identify any conversion factors.

•How should the answer look?

2.5 mol NaCl = gCl2

• What is unique to the problem?

88.625

= 89 gCl2

1 mol Cl2

2 mol NaCl 70.9 g Cl2

1 mol Cl2

Factor conversion method:

5 - 49GS105

H2OH2O

more stablemore stable


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

-486 kJ made

5 - 50GS105

Bond Energy2H2 + O22H2 + O2 2H2O + Energy2H2O + Energy

2H-H + O=O 2 H-O-H

2 (436)

498

4 (464)

1370 kJ used

1856 kJ made- = -486 kJ made

5 - 51GS105

Exothermic ReactionsE

ner

gy

Rxn Progress

2Mg + O2 2MgO + Energy

2H2 + O2 2H2O + Energy

CH4 + 2O2 CO2 + 2H2O + Energy

-486 kJ made

5 - 52GS105

Bond EnergyCH4 + 2O2CH4 + 2O2 CO2 CO2

4C-H + 2O=O O=C=O + 2 H-O-H

4 (414)

2(498)

2 (799)

2652 kJ used

3454 kJ made-

= - 802 kJ made

+ 2H2O + Energy + 2H2O + Energy

4 (464)

5 - 53GS105

more stablemore stable


Endothermic reactionEndothermic reaction

+H= heat of reactionEn

erg

y

Rxn Progress

Reactants

Products

Eact= Activation Energy

(Gets cold)(Gets cold)

5 - 54GS105

En

erg

y

Rxn Progress

Endothermic ReactionsEnergy is required

Products are less stable.

Products(Water)

Reactants(Ice)

+DH

5 - 55GS105

Exothermic ReactionsE

ner

gy

Rxn Progress

Reactants(Water)

Products(Ice)

Energy is released

Products are more stable.

-DH

5 - 56GS105

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 - 57GS105

Paper burning Paper burning

Paper yellowingPaper yellowing

Reaction RatesFast:

Slow: Human AgingHuman Aging

ExplosionExplosion

Fruit RipeningFruit Ripening

Nails rustingNails rusting

5 - 58GS105

• They have to have enough E.

Reaction Rates

For reactants to make products:• Molecules must collide

(If they don’t meet they can’t react: • solvents really help)

• They have to be aligned correctly.

(Parked cars don’t collide)

(Car bumpers meeting don’t make a change)

5 - 60GS105

Reaction Rates

Factors that increase reaction rate:1. More Reactants (Greater Concentration) :

More cars More collisions

8 blocks:34 surfaces

8 blocks:24 surfaces

More surface area More collisions

5 - 61GS105

Reaction Rates

Factors that increase reaction rate:2. Higher Temperature:

Faster cars More collisions

More Energy More collisions

Need Energy of Activation (Eact)

5 - 62GS105

Reaction Rates

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

Lower Eact More collisions

Uncatalysed reactionUncatalysed reaction

5 - 63GS105

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

5 - 64GS105

Platinum as catalyst– Hydrogen peroxide decomposes slowly In water, but very quickly with the addition of platinum

Catalysts

5 - 65GS105

Without added energy reactions go to disorder

Entropy = The amount of disorder:

Entropy

Randomness factorNature tends to move spontaneously from a state of lower probably to one of higher probability.

If a beaker with marbles is shaken, which beaker (above) will result?

5 - 1GS105 CHGS105 Chapter 17 Chemical Reactions Chemical Changes Chemical Equations Types of...

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