5 - 1GS105 CHGS105 Chapter 17 Chemical Reactions Chemical Changes Chemical Equations Types of Reactions Oxidation-ReductionMoles Energy in Chemical Reactions.
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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:
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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)
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Law of Conservation of MatterQuestion:
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Law of Conservation of MatterSolution: Fe + O2 Fe2O3
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Law of Conservation of MatterQuestion:
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Law of Conservation of MatterSolution:
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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 - 13GS105
Ca
H
Cl
Balancing Equations
Ca + HCl CaCl2 + H2 Ca + HCl CaCl2 + H2
•Reactants •Products
Step 1: Count atoms of each element on both sides of equation.
1
1
1
1
2
2
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Balancing Equations
Ca + HCl CaCl2 + H2 Ca + HCl CaCl2 + H2
Ca
H
Cl
Ca
H
Cl
•Reactants •Products
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
Ca + HCl CaCl2 + H2 Ca + HCl CaCl2 + H2
•Reactants •Products
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
•Reactants •Products
Step 1: Count atoms of each element on both sides of equation.
31412
1 2831
5 - 17GS105
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 - 18GS105
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 - 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
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 - 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
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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 - 22GS105
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
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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 - 24GS105
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 - 25GS105
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 - 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:
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___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
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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
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
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
Ratios in Chemical Equations
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
Ratios in Chemical Equations
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)
How many gs of O2 are needed to make 11 g CO2?
Factor conversion method:
5 - 45GS105
Ratios in Chemical Equations
11 g CO2 = g O2 8 32 g O2
44 g CO2
C(s) + O2 (g) CO2(g)
How many gs of O2 are needed to make 11 g CO2?
? 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
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
-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
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 - 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
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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
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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?
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