Unit 8 Chemical Reactions
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Transcript of Unit 8 Chemical Reactions
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Unit 8 Unit 8 Chemical ReactionsChemical Reactions
Unit 8 Unit 8 Chemical ReactionsChemical Reactions
PAGE 123PAGE 123
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Describing Chemical Reactions
• A chemical reaction is the process by which one or more substances are changed into one or more different substances.
•They are described by chemical equations
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Describing Chemical Reactions
• In a chemical reaction:– bonds are broken in the reactants
–Bonds are formed in the products
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Parts of a Chemical Parts of a Chemical EquationEquation
Parts of a Chemical Parts of a Chemical EquationEquation
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Reactants•original substances in a chemical reaction
•written on the left hand side of a chemical equation
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Products•The resulting substances produced in a chemical reaction.
•written on the right hand side of the chemical equation
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yields
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Subscripts in (parenthesis)
•represents the physical states of the compounds (elements)
•Ex: (s)= solid, (l)=liquid, (g)= gas, (aq)= aqueous (dissolved in water)
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•Words or symbols are placed over/under the arrow(s) to indicate certain conditions under which the reaction is carried out.
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– : heat is applied– catalyst
• substance that speeds up a chemical reaction without becoming part of the reaction.
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Law of conservation of mass
According to the law ofconservation of mass, •the total mass of reactants must equal the total mass of products for any given chemical reaction.
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Law of conservation of mass
Mass must be equal50 g + 45 g
Balance atoms H2 (g) + O2 (g) H2O (g)22
95g
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Translate Chemical Translate Chemical Equations into WordsEquations into WordsTranslate Chemical Translate Chemical
Equations into WordsEquations into Words
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Chemical Equations
•1) include all of the symbols appearing in the equation (with the exception of the
coefficients)
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Chemical Equations•3. Diatomic Elements: Elements that combine with each other when found alone in nature
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Diatomic Elements•7 diatomic elements (know)
H2 O2 F2 Br2 I2 N2 Cl2
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Example #2Mg(s) + 2HCl(aq) MgCl2(aq) +
H2(g)Solid magnesium
reacts with
aqueous hydrochloric acid
to produceaqueous magnesium
chlorideand hydrogen gas
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Check for Understanding
CaCO3(s) CaO(s) + CO2(g)
Solid calcium carbonate is heated and produces solid calcium oxide and gaseous carbon dioxide
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Check for Understanding #2
3KOH(aq) + Fe(NO3)3(aq) Fe(OH)3(s) + 3KNO3(aq)
Aqueous potassium hydroxide reacts with aqueous iron (III) nitrate to produce solid iron (III) hydroxide and aqueous potassium nitrate
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Writing Chemical Equations Writing Chemical Equations from a Written from a Written
DescriptionDescription
Writing Chemical Equations Writing Chemical Equations from a Written from a Written
DescriptionDescription
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Example #1
Aluminum metal reacts with oxygen in the air to form solid aluminum oxide.
4 Al (s) + O2 (g)3 Al2O3 (s)2
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Example #2
When solid mercury(II) sulfide is heated with oxygen gas, liquid mercury metal and gaseous sulfur dioxide are produced.
+ SO2 (g)HgS (s) + O2
(g)
Hg (l)
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Check for Understanding
Oxygen gas can be produced by heating solid potassium chlorate in the presence of the catalyst manganese dioxide. Potassium chloride is a solid residue.
MnO2 + O2 (g)2 2 3KClO3 (s) KCl (s)
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Check for Understanding
Aqueous potassium nitrate and a precipitate of barium chromate are formed when aqueous solutions of barium nitrate and potassium chromate are mixed.
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Check for Understanding
Aqueous potassium nitrate and a precipitate of barium chromate are formed when aqueous solutions of barium nitrate and potassium chromate are mixed.
Ba(NO3)2 (aq) + K2CrO4 (aq)
KNO3 (aq) + BaCrO4 (s)2
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Types of Chemical Types of Chemical ReactionsReactions
Types of Chemical Types of Chemical ReactionsReactions
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Synthesis (Combination) Reactions
Two or more substances combine to form a new compound.
.
Formation of only ONE product.
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Synthesis (Combination) Reactions
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Examples:
2H2 + O2 2H2O
CaO + H2O Ca(OH)2
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Decomposition Reactions
• A single compound undergoes a reaction that produces two or more simpler substances.
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Decomposition Reactions
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Decomposition Reactions Decomposition reactions are the opposite of synthesis reactions.
There is only one reactant.
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Examples
•CaCO3 CaO + CO2
•Na2CO3 Na2O + CO2
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Single-Replacement Reactions
• one element replaces a similar element in a compound.
• a single element reacts with a compound.
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Single-Replacement Reactions
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Distinguishing Characteristics
• Examples:
Pb + 2HNO3 Pb(NO3)2 + H2
F2 + 2NaI 2NaF + I2
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Predict the Products
Zn + CuCl2 ZnCl2 + Cu
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Double Replacement Reactions
The ions of two compounds exchange places in an aqueous solution to form two new compounds.
Two ionic compounds “swap” ions.
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Double Replacement Reactions
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Usually forms a precipitate
• precipitate: when two aqueous solutions are mixed and a solid product that is formed
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Precipitate
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Examples
• PbSO4 + 2KCl K2SO4 + PbCl2
• AgNO3(aq) + KCl(aq) ‑‑‑‑> AgCl(s) + KNO3(aq)
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Predict the Products
H2O 2KOH + H2SO4 K2SO4 +2HOH
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Combustion Reactions
A hydrocarbon (CxHy) combines with oxygen, releasing a large amount of energy in the form of light and heat.
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General Form
CxHy + O2 CO2 + H2O
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Example
• C3H8 + 5O2 3 CO2 + 4 H2O
• CH4 + O2 CO2 + H2O
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Predict the Products
H2O C2H6 + O2 CO2+2 4 12101 5 2 6
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1) 2 Li + 2 H2O 2 LiOH + H2
single replacement / displacement
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2) NH4Cl NH3 + HCl
decomposition
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3) AgNO3 + NaCl AgCl + NaNO3
double replacement / displacement
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4) 2 C6H14 + 19 O2 12 CO2 + 14 H2O
combustion
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5) N2 + 3 H2 2 NH3
combination / synthesis
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Oxidation – Oxidation – ReductionReductionProcessesProcesses
Oxidation – Oxidation – ReductionReductionProcessesProcesses
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Redox ReactionAny chemical reaction that involves the transfer of one or more electrons between atoms. One reactant gains electrons and the other reactant loses electrons.
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Examples of Redox Reactions
•Combustion of gasoline •Burning of wood•Energy from food•Bleaching stains•Iron rusting
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Oxidation and Reduction
• Opposing reactions
•Must occur together–Redox (Reduction – Oxidation)
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Oxidation•Electrons are fully or partially
lost
Mg0 (s) Mg 2+ + 2e-
Electrons lost: written as a product
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Reduction• Electrons are fully or
partially gained
S0(s) + 2 e- S2-
electrons gained: written as a reactant
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Mnemonic Device
• LEO the lion goes GER
LEO: Loss of Electrons is Oxidation
GER: Gain of Electrons is Reduction
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Mnemonic Device
•OIL RIG
–Oxidation Is Loss of electrons
–Reduction Is Gain of electrons
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Complete Redox Reaction
• Add together the reduction half-reaction with the oxidation half-reaction to get the complete redox reaction.
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Complete Redox Reaction
Mg0 (s) Mg 2+ + 2e-
S0(s) + 2 e- S2-
+
Mg0 (s) + S0
(s) Mg 2+ + S2-
Mg + S Mg+2+ S -2
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Assigning Oxidation Assigning Oxidation NumbersNumbers
Assigning Oxidation Assigning Oxidation NumbersNumbers
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Oxidation Numbers•Numbers assigned to all of
the elements involved in the reaction to determine if electrons have been transferred between atoms in a reaction.
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Oxidation Numbers
• The oxidation number is usually equal to the charge on the ion if it was formed.
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Rule #1•Free elements are assigned
an oxidation state of 0.
–Al = 0–Na = 0
–H2 = 0
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Rule #2• The oxidation state for any
simple one-atom ion is equal to its charge.
–Na+ = +1–Be2+= +2–F- = -1
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Rule #3•The alkali metals (Li, Na, K, Rb,
Cs and Fr) in compounds are always assigned an oxidation state of +1.
–LiOH: Li = +1–Na2SO4: Na= +1
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Rule #4
•Fluorine in compounds is always assigned an oxidation state of -1.
–HF: F= -1
–MgF2: F= -1
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Rule #5• The alkaline earth metals (Be,
Mg, Ca, Sr, Ba, and Ra) and also Zn and Cd in compounds are always assigned an oxidation state of +2. Similarly, Al & Ga are always +3.
•MgF2: Mg = +2
•CaO: Ca= +2
•Al2O3: Al=+3
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Rule #6• Hydrogen in compounds is assigned an
oxidation state of +1.
Exception - Hydrides, ex. LiH (H=-1).
•H2SO4: H=+1
•HCl: H=+1
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Rule #7
• Oxygen in compounds is assigned an oxidation state of -2.
Exception - Peroxide, ex. H2O2 (O = -1).
– H3PO4: O=-2
– H2O: O=-2
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Rule #8
•The sum of the oxidation numbers of all atoms in a neutral compound is 0.
–H2SO4: add up to 0–CO2: add up to 0
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Rule #9
•The sum of the oxidation numbers of all atoms in a polyatomic ion equals the charge on the ion.
–SO42-: add up to -2
–NH4+: add up to +1
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Examples•Al(s):
–Al = ____
Rule #1
0
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Examples•CaCl2:
–Ca = ____–Cl=____
Rule #5
Ca+2 Rule #8
1 (+2) + 2 (Cl) = 0
Cl = -1
-1
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Examples•HNO3:
–H= ____–N= ____–O= ____
Rule # 6
Rule # 7
Rule # 8+1
-2 1(1) + 1(N) + 3(-2) = 0
N = +5
+5
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Examples• SO4
2-:
– S= ____– O= ____
Rule #7
-2
Rule #9
1(S) + 4(-2) = -2+6
S= +6
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Examples• H2O:
– H= ____– O= ____
Rule #6
+1Rule #7
-2
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Examples•(NH4)2CO3
NH4+ CO3
2-
N=____ C=___ H=____ O=___
Rule 6
+1
Rule 7
-2
Rule 9
1(N)+4(+1)=+1N= -3
-3
1(C)+3(-2)=-2C=+4
+4
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Check for Understanding
• S8:
– S= ____
• AsO43-:
– As= ____ – O= ____
0
-2+5
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Check for Understanding
• Cr(OH)3:
– Cr= ____ – O= ____ – H= ____
-2
+1
+3
OH-
![Page 94: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/94.jpg)
Check for Understanding
• (NH4)3PO4:
– N= ____ – H=_____ – P= ____ – O= ____
NH4+ PO4
-3
+1-3
-2
+5
![Page 95: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/95.jpg)
Oxidized Element
• Atoms that lose electrons in a chemical reaction.
– Elements that lose electrons are undergoing oxidation and are said to be oxidized.
![Page 96: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/96.jpg)
Oxidized Element
• The substance that loses electrons is the oxidized element.
• Atoms that are oxidized will have an increase in their oxidation number
![Page 97: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/97.jpg)
Oxidized Element
Mg0 (s) + S0
(s) Mg 2+ + S2-
Increase in oxidation number
Mg is oxidized
![Page 98: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/98.jpg)
Reduced Element
• Atoms that gain electrons in a chemical reaction.
– Elements that gain electrons are undergoing reduction and are said to be reduced.
![Page 99: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/99.jpg)
Reduced Element
• The substance that gains electrons is the reduced element.
• Atoms that are reduced will have an decrease in their oxidation number
![Page 100: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/100.jpg)
Reduced Element
Mg0 (s) + S0
(s) Mg 2+ + S2-
Decrease in oxidation number
S is reduced
![Page 101: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/101.jpg)
Oxidizing Agent•The element or compound that
is reduced.
•It is called the oxidizing agent because it oxidizes the other element or compound.
![Page 102: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/102.jpg)
Oxidizing Agent
Mg0 (s) + S0
(s) Mg 2+ + S2-
Decrease in oxidation number
S is reduced
S is the oxidizing agent(it is oxidizing Mg)
![Page 103: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/103.jpg)
Reducing Agent•The element or compound that
is oxidized.
• It is called the reducing agent because it reduces the other element or compound.
![Page 104: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/104.jpg)
Reducing Agent
Mg0 (s) + S0
(s) Mg 2+ + S2-
Increase in oxidation number
Mg is oxidizedMg is the reducing agent
(it is reducing S)
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Examples
• Are the following redox reactions?
• If yes:– What element is oxidized?– What element is reduced?– What is the oxidizing agent?– What is the reducing agent?
![Page 106: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/106.jpg)
Examples
Mg(s) + S(s) MgS
Step #1: Assign Oxidation Numbers
0 0 +2-2
Step # 2: Do the oxidation numbers change?
- if no it is not a redox reaction
- if yes it is a redox reaction
Yes – It is a redoxWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
MgS
SMg
![Page 107: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/107.jpg)
Examples
Step #1: Assign Oxidation Numbers
2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag(s)
0 0
NO3- NO3
-
+1 +2
Yes – It is a redox
Step # 2: Do the oxidation numbers change?
- if no it is not a redox reaction
- if yes it is a redox reaction
What element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
CuAg
AgNO3(aq)
Cu(s)
![Page 108: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/108.jpg)
Check for Understanding
• Are the following redox reactions?• If yes:
– What element is oxidized?– What element is reduced?– What is the oxidizing agent?– What is the reducing agent?
![Page 109: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/109.jpg)
Check for Understanding
4Fe(s) + 3O2(g) 2Fe2O3(s)
0 0 -2+3
YesWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
FeOO2
Fe
![Page 110: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/110.jpg)
Check for Understanding
Ca(s) + H2O(l) Ca(OH)2(aq) + H2(g)
0 0+1 -2
OH-
+2 +1-2
YesWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
CaH
H2OCa
![Page 111: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/111.jpg)
Check for Understanding
HCl + NaOH NaCl + H2O +1-1 +1-2+1 +1-1 +1 -2
No – it is not a redox
![Page 112: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/112.jpg)
Check for Understanding
Fe2O3(s) + 3CO(g) 2Fe(s) + 3CO2(g)
-2 +2-2 0+3 +4-2
YesWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
CFe
Fe2O3
CO
![Page 113: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/113.jpg)
Check for Understanding
2AgNO3(aq) + Cu(s) Cu(NO3)2(aq) + 2Ag (s)
NO3- NO3
-
+1 0 +2 +0
YesWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
CuAg
AgNO3Cu
![Page 114: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/114.jpg)
Check for Understanding
NaCl + AgNO3 NaNO3 + AgCl+1-1 +1
NO3- NO3
-
+1 +1-1
No – it is not a redox
![Page 115: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/115.jpg)
Check for Understanding
2 H2(g) + O2(g) 2 H2O(l)
0 0 +1-1
YesWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
HO
O2H2
![Page 116: Unit 8 Chemical Reactions](https://reader035.fdocuments.in/reader035/viewer/2022062221/568131de550346895d98443b/html5/thumbnails/116.jpg)
Check for Understanding
CH4 + 2 O2 CO2 + 2 H2O -4+1 0 +4-2 +1-2
YesWhat element is oxidized?What element is reduced?What is the oxidizing agent?What is the reducing agent?
CO
O2
CH4