Download + O 2 (g)

5.1 Introduction to Chemical Reactions
A. General Features of Physical and Chemical
Changes
• A chemical change (a chemical reaction) converts
one substance into another.
• Chemical reactions involve:
1. Breaking bonds in the reactants (starting
materials)
2. Forming new bonds in the products
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5.1 Introduction to Chemical Reactions
A. General Features of Physical and Chemical
Changes
2
5.1 Introduction to Chemical Reactions
B. Writing Chemical Equations
A chemical equation uses chemical formulas and other
symbols showing what reactants are the starting
materials in a reaction and what products are formed.
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5.1 Introduction to Chemical Reactions
B. Writing Chemical Equations
• The law of conservation of mass states that
atoms cannot be created or destroyed in a
chemical reaction.
4
5.1 Introduction to Chemical Reactions
B. Writing Chemical Equations
5
5.2 Balancing Chemical Equations
HOW TO Balance a Chemical Equation
Example Write a balanced chemical equation for
the reaction of propane (C3H8) with
oxygen (O2) to form carbon dioxide (CO2)
and water (H2O).
Step [1] Write the equation with the correct formulas.
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5.2 Balancing Chemical Equations
HOW TO Balance a Chemical Equation
Step [2] Balance the equation with coefficients one
element at a time.
• Balance the C’s first:
• Balance the H’s next:
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5.2 Balancing Chemical Equations
HOW TO Balance a Chemical Equation
Step [2] Balance the equation with coefficients one
element at a time.
• Finally, balance the O’s:
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Balance the Equations
1. __H2 + __O2  __H2O
2. __NO + __O2  __NO2
3. __CH4 + __Cl2  __CH2Cl2 + __HCl
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Polyatomic Ions
__Ca3(PO4)2 + __H2SO4  __CaSO4 + __H3PO4
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Balance the Equation
__Al + __H2SO4  __Al2(SO4)3 + __H2
__Na2SO3 + __H3PO4  __H2SO3 + __Na3PO4
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Balance the Equation
__Mg + __HBr  __MgBr2 + __H2
__KClO3  __KCl + __O2
__CH4 + __Cl2  __CCl4 + __HCl
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Balance the Equation
__Al2O3 + __HCl  __AlCl3 + __H2O
__Al(OH)3 + __H2SO4  __Al2(SO4)3 + __H2O
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__Ni + __HCl  __NiCl2 + __H2
__PbS + __O2  __PbO + __SO2
__H3PO4 + __Ca(OH)2  __Ca3(PO4)2 + __H2O
__H2SO4 + __NaOH  __Na2SO4 + __H2O
__CO + __O2  __CO2
__S + __O2 + __H2O  __H2SO4
5.3 Types of Reactions
The majority of chemical reactions fall into 6 categories:
• combination
• decomposition
• single replacement
• double replacement
• oxidation and reduction (Section 5.4)
• acid-base (Chapter 9)
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5.3 Types of Reactions
A. Combination and Decomposition
• A combination reaction is the joining of two or more
reactants to form a single product.
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5.3 Types of Reactions
A. Combination and Decomposition
• A decomposition reaction is the conversion of a
single reactant to two or more products.
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5.3 Types of Reactions
B. Replacement Reactions
• A single replacement reaction is a reaction in which
one element replaces another element in a
compound to form a different compound and
element as products.
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5.3 Types of Reactions
B. Replacement Reactions
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5.3 Types of Reactions
B. Replacement Reactions
• A double replacement reaction is a reaction in
which two compounds exchange “parts”–atoms or
ions—to form two new compounds.
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5.3 Types of Reactions
B. Replacement Reactions
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Combination, Decomposition, Single
Displacement or Double Displacement?
Ni(NO3)2 + Mg  Ni + Mg(NO3)2
2 KI + Sn(NO3)2  SnI2 + 2 KNO3
2 HgO  2 Hg + O2
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Predicting Reactions
Combination: N2 + ____  Mg3N2
Decomposition: 2 SO3  2SO2 + ______
Single Replacement: 2 Ag + CuBr2  ______ + ______
Double Replacement: KOH + HI  ______ + _______
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5.4 Oxidation and Reduction
A. General Features
• Oxidation is the loss of electrons from an atom.
• Reduction is the gain of electrons by an atom.
• Both processes occur together in a single
reaction called an oxidation−reduction or redox
reaction.
• A redox reaction involves the transfer of electrons
from one element to another.
• A redox reaction always has two components,
one that is oxidized and one that is reduced.
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5.4 Oxidation and Reduction
A. General Features
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5.4 Oxidation and Reduction
A. General Features
Zn + Cu2+
Zn2+ + Cu
Each of these processes can be written as an
individual half reaction:
Oxidation half reaction:
Reduction half reaction:
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5.4 Oxidation and Reduction
A. General Features
Zn
+ Cu2+
oxidized reduced
Zn2+ + Cu
A compound that is reduced while causing another
compound to be oxidized is called an oxidizing agent.
•Cu2+ acts as an oxidizing agent because it causes
Zn to lose electrons and become oxidized.
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5.4 Oxidation and Reduction
A. General Features
Zn
+ Cu2+
oxidized reduced
Zn2+ + Cu
A compound that is oxidized while causing another
compound to be reduced is called a reducing agent.
•Zn acts as a reducing agent because it causes
Cu2+ to gain electrons and become reduced.
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5.4 Oxidation and Reduction
A. General Features
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5.4 Oxidation and Reduction
B. Examples of Oxidation–Reduction Reactions
Iron Rusting
O gains e– and is reduced.
4 Fe(s) + 3 O2(g)
neutral Fe neutral O
2 Fe2O3(s)
Fe3+ O2–
Fe loses e– and is oxidized.
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5.4 Oxidation and Reduction
B. Examples of Oxidation–Reduction Reactions
Zn + 2 MnO2
ZnO + Mn2O3
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Zn + 2H+  Zn2+ + H2
Fe3+ + Al  Al3+ + Fe
I- + Br2  I2 + Br-
AgBr  Ag + Br2
5.4 Oxidation and Reduction
B. Examples of Oxidation–Reduction Reactions
Oxidation results in the:
Reduction results in the:
• Gain of oxygen atoms
• Loss of oxygen atoms
• Loss of hydrogen atoms
• Gain of hydrogen atoms
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5.5 The Mole and Avogadro’s Number
A mole is a quantity that contains 6.02 x 1023 items.
• 1 mole of C atoms = 6.02 x 1023 C atoms
• 1 mole of H2O molecules = 6.02 x 1023 H2O molecules
• 1 mole of Vitamin C molecules = 6.02 x 1023 Vitamin C
molecules
The number 6.02 x 1023 is Avogadro’s number.
1.3×1023 kg
Titan, largest moon of Saturn
1.5×1023 kg
Ganymede, largest moon of Jupiter
3.3×1023 kg
Mercury
6.4×1023 kg
Mars
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How many items do 1 mol of the
following contain:
• Baseballs
• Bicycles
• Cheerios
• CH4 molecules
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5.5 The Mole and Avogadro’s Number
It can be used as a conversion factor to relate the
number of moles of a substance to the number of
atoms or molecules:
1 mol
6.02 x 1023 atoms
or
6.02 x 1023 atoms
1 mol
1 mol
or 6.02 x 1023 molecules
6.02 x 1023 molecules
1 mol
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5.5 The Mole and Avogadro’s Number
Sample Problem 5.5
How many molecules are contained in 5.0 moles
of carbon dioxide (CO2)?
Step [1] Identify the original quantity and the
desired quantity.
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5.5 The Mole and Avogadro’s Number
Step [2]
Write out the conversion factors.
Step [3] Set up and solve the problem.
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How many C atoms are there in the
following:
• 2.0 mol
• 6.0 mol
• 0.5 mol
• 25.0 mol
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How many molecules are contained in
each of the following number of moles
• 2.5mol of penicillin
• 0.25 mol of NH3
• 0.4 mol of Sugar
• 55.3 mol of Acetaminophen
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5.6 Mass to Mole Conversions
• The formula weight is the sum of the atomic weights
of all the atoms in a compound, reported in atomic
mass units (amu).
HOW TO Calculate the Formula Weight of a Compound
Example Calculate the formula weight for FeSO4.
Step [1]
Write the correct formula and determine
the number of atoms of each element from
the subscripts.
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5.6 Mass to Mole Conversions
HOW TO Calculate the Formula Weight of a Compound
Step [2]
Multiply the number of atoms of each
element by the atomic weight and add
the results.
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5.6 Mass to Mole Conversions
A. Molar Mass
• The molar mass is the mass of one mole of
any substance, reported in grams per mole
(g/mol).
• The value of the molar mass of a compound in
grams equals the value of its formula weight
in amu.
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5.6 Mass to Mole Conversions
B. Relating Grams to Moles
• The molar mass relates the number of moles
to the number of grams of a substance.
• In this way, molar mass can be used as a
conversion factor.
• The molar mass of H2O is 18.0 g/mol, the
conversion factor can be written:
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5.6 Mass to Mole Conversions
B. Relating Grams to Moles
Sample Problem 5.9
How many moles are present in 100. g of aspirin
(C9H8O4)?
Step [1]
Calculate the molar mass.
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5.6 Mass to Mole Conversions
B. Relating Grams to Moles
Step [2]
Write out the conversion factors.
•The conversion factor is the molar mass, and it
can be written in two ways.
•Choose the one that places the unwanted unit,
grams, in the denominator so that the units cancel:
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5.6 Mass to Mole Conversions
B. Relating Grams to Moles
Step [3]
Set up and solve the problem.
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How many moles are contained in the
following:
100 g NaCl
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How many moles are contained in the
following:
0.25g Aspirin(C9H8O4)
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How many moles are contained in the
following:
25.5g CH4
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How many moles are contained in the
following:
25g of H2O
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5.6 Mass to Mole Conversions
C. Relating Grams to Number of Atoms or
Molecules
We can also use the molar mass to show the
relationship between grams and number of
molecules (or atoms).
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5.6 Mass to Mole Conversions
C. Relating Grams to Number of Atoms or
Molecules
Sample Problem 5.10
How many molecules are in a 325-mg tablet of
aspirin (C9H8O4)?
Step [1]
Find the molar mass
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5.6 Mass to Mole Conversions
C. Relating Grams to Number of Atoms or
Molecules
Step [2]
Write out the conversion factors.
59
5.6 Mass to Mole Conversions
C. Relating Grams to Number of Atoms or
Molecules
Step [3]
Set up and solve the problem.
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How many molecules are present in a 500mg
tablet of penicillin (C16H18N2O4S)
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How many molecules are present in a 500mg
tablet of penicillin (C16H18N2O4S)
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How many molecules are present in a 750mg of Mescaline
(Hallucinogenic from peyote) (C11H17NO3)
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5.7 Mole Calculations in Chemical
Equations
A balanced chemical equation also tell us:
• The number of moles of each reactant that combine
• The number of moles of each product formed
1 N2(g)
+
1 O2(g)
2 NO(g)
(The coefficient “1” has been written for emphasis.)
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5.7 Mole Calculations in Chemical
Equations
Coefficients are used to form mole ratios, which can
serve as conversion factors.
N2(g)
+
O2(g)
2 NO(g)
Mole ratios:
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5.7 Mole Calculations in Chemical
Equations
Sample Problem 5.11
Using the balanced chemical equation, how
many moles of CO are produced from 3.5 moles
of C2H6?
2 C2H6(g) + 5 O2(g)
Step [1]
4 CO(g) + 6 H2O(g)
Identify the original and desired quantities.
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5.7 Mole Calculations in Chemical
Equations
2 C2H6(g) + 5 O2(g)
Step [2]
4 CO(g) + 6 H2O(g)
Write out the conversion factors.
Step [3] Set up and solve the problem.
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Complete the following conversions
N2(g)
+
O2(g)
2 NO(g)
• How many mol of NO are formed from 3.3 mol of N2
• How many mol of NO are formed from 0.5mol of O2
• How many moles of O2 are needed to completely react
with 1.2 mol of N2
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N2(g)
+
O2(g)
2 NO(g)
• How many mol of NO are formed from 3.3 mol of N2
• How many mol of NO are formed from 0.5mol of O2
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N2(g)
+
O2(g)
2 NO(g)
• How many moles of O2 are needed to completely react
with 1.2 mol of N2
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Example
Using the balanced equation, how many
grams of O3 are formed from 9.0 mol of O2.
3 O2(g)
sunlight
2 O3(g)
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Step [1]
Convert the number of moles of reactant
to the number of moles of product using
a mole–mole conversion factor.
3 O2(g)
sunlight
2 O3(g)
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
Step [2]
Convert the number of moles of product
to the number of grams of product using
the product’s molar mass.
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Moles of Reactant to Grams of Product
•Set up and solve the conversion.
3 O2(g)
sunlight
2 O3(g)
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C6H12O6
(glucose)
2 C2H6O + 2CO2
(ethanol)
• How many g of ethanol are formed from 0.55 mol of
glucose
• How many g of CO2 are formed from 0.25 mol of glucose
• How many g of glucose are needed to form 1mol of
ethanol
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How many g of ethanol are formed from
0.55 mol of glucose
C6H12O6
2 C2H6O + 2CO2
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How many g of CO2 are formed from
0.25 mol of glucose
C6H12O6
2 C2H6O + 2CO2
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How many mol of ethanol would be formed if
5g of glucose is used
C6H12O6
2 C2H6O + 2CO2
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
Example
Ethanol (C2H6O) is synthesized by reacting
ethylene (C2H4) with water.
How many grams of ethanol are formed
from 14 g of ethylene?
C2H4 + H2O
C2H6O
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
C2H4 + H2O
C2H6O
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
C2H4 + H2O
C2H6O
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5.8 Mass Calculations in Chemical Equations
HOW TO Convert Grams of Reactant to Grams of Product
C2H4 + H2O
C2H6O
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2 C2H6(g) + 5 O2(g)
4 CO(g) + 6 H2O(g)
• 1) How many molecules of CO is
produced?
• 2) How many g of C2H6 are needed to
react with all of O2
• 3) How many g of H2O are produced when
15g of O2 is used.
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2 C2H6(g) + 5 O2(g)
4 CO(g) + 6 H2O(g)
How many molecules of CO is produced?
2 C2H6(g) + 5 O2(g)
4 CO(g) + 6 H2O(g)
How many g of C2H6 are needed to react with all of O2
2 C2H6(g) + 5 O2(g)
4 CO(g) + 6 H2O(g)
How many g of H2O are produced when 15g of O2 is used.
5.9 Percent Yield
• The theoretical yield is the amount of product
expected from a given amount of reactant
based on the coefficients in the balanced
chemical equation.
• Usually, however, the amount of product
formed is less than the maximum amount of
product predicted.
• The percent yield is the amount of product
isolated from a reaction.
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5.9 Percent Yield
Sample Problem 5.14
If the reaction of ethylene with water to form
ethanol has a calculated theoretical yield of 23 g
of ethanol, what is the percent yield if only 15 g
of ethanol are actually formed?
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5.10 Limiting Reactants
• The limiting reactant is the reactant that is
completely used up in a reaction.
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5.10 Limiting Reactant
A. Determining the Limiting Reactant
Analyze the two possible outcomes:
• If the amount present of the second reactant
is less than what is needed, the second
reactant is the limiting reagent.
• If the amount present of the second reactant is
greater than what is needed, the second
reactant is in excess.
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5.10 Limiting Reactant
C. Determining the Limiting Reactant Using the
Number of Grams
Sample Problem 5.20
Using the balanced equation, determine the limiting
reactant when 10.0 g of N2 (MM = 28.02 g/mol) react
with 10.0 g of O2 (MM = 32.00 g/mol).
N2(g) + O2(g)
2 NO(g)
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5.10 Limiting Reactant
C. Determining the Limiting Reactant Using the
Number of Grams
Sample Problem 5.20
[1] Convert the number of grams of each reactant
into moles using the molar masses.
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5.10 Limiting Reactant
C. Determining the Limiting Reactant Using the
Number of Grams
Sample Problem 5.20
[2] Determine the limiting reactant by choosing N2
as the original quantity and converting to mol O2.
mole–mole
Conversion factor
0.357 mol N2 x
1 mol O2
1 mol N2
= 0.357 mol O2
The amount of O2 we started with (0.313 mol) is
less than the amount we would need (0.357 mol) so
O2 is the limiting reagent.
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N2(g) + O2(g)  NO(g)
• Determine the limiting reactant under the
following conditions:
• 1) 12.5g N2 and 15.0g O2
• 2) 14.0g N2 and 13.0g O2
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N2(g) + O2(g)  NO(g)
12.5g N2 and 15.0g O2
N2(g) + O2(g)  NO(g)
14.0g N2 and 13.0g O2
Balance/Rxn Type/ REDOX
1. Ni + HCl  NiCl2 + H2
2. CH4 + Cl2  CCl4 + HCl
3. KClO3  KCl + O2
4. Al2O3 + HCl  AlCl3 + H2O
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101
Given the following reaction:
C12H22O11 + H2O  C2H6O + CO2
(sucrose)
(ethanol)
1. Balance the equation
2. Determine the molecular weight of sucrose
3. How many mols of Ethanol would be produced
from 2 mols of sucrose?
4. How many g of ethanol would be produced from
17.1 g sucrose?
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