Transcript Chemical Reaction

General, Organic, and
Biological Chemistry
Fourth Edition
Karen Timberlake
Chapter 6
Chemical Reactions
and Quantities
6.1
Equations for
Chemical Reactions
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Lectures
Chemical Change
A chemical change occurs
when a substance is
converted into one or more
new substances.
Chemical changes can be
recognized by
 a change in color,
 the formation of a solid, or
 the formation of bubbles.
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Chapter 6, Section 1
A chemical change produces new
substances. When silver (Ag)
reacts with sulfur (S), it produces
silver sulfide (Ag2S).
2
Evidence of Chemical Change
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Chapter 6, Section 1
3
Learning Check
Identify the visible evidence of a chemical
reaction in each of the following:
1. Methane gas in an outdoor heater burns with
a blue flame.
2. Bleach removes stains from a shirt.
3. Bubbles of CO2 are released when baking
soda is mixed with vinegar.
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Chapter 6, Section 1
4
Solution
Identify the visible evidence of a chemical
reaction in each of the following:
1. Methane gas in an outdoor heater burns with
a blue flame.
heat and a flame
2. Bleach removes stains from a shirt.
color change (color removed)
3. Bubbles of CO2 are released when baking
soda is mixed with vinegar.
formation of gas (bubbles)
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Chapter 6, Section 1
5
Chemical Reactions
A chemical reaction
 involves the rearrangement of
atoms.
 produces one or more new
substances.
 can be observed by the
appearance of new physical
properties.
A chemical reaction forms new
products with different properties.
An antacid (NaHCO3) tablet
in water forms bubbles of carbon
dioxide (CO2).
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Chapter 6, Section 1
6
Writing a Chemical Equation
A chemical equation tells us what substances react
(reactants) and what substances are formed
(products).
C(s) + O2(g)
reactants
CO2(g)
product
(+) used when there is two or more products or reactants
heat is used to start the reaction
(s) the compound is a solid
(l) the compound is a liquid
(g) the compound is a gas
(aq) aqueous, the compound is dissolved in water
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Chapter 6, Section 1
7
Equation for a Chemical Reaction
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Chapter 6, Section 1
8
Balanced Chemical Equations
In a balanced chemical equation, the number of
atoms in the reactants is equal to the number of atoms
in the products for each element.
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Chapter 6, Section 1
9
Balancing Chemical Equations
To balance a chemical equation,
 whole number coefficients are placed in front of
the chemical formulas.
 coefficients in front of a molecule represent the
multiple of that molecule needed in a balanced
reaction.
 subscripts are never changed.
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Chapter 6, Section 1
10
Checking a Balanced Equation
Reactants
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Products
Atoms C
1
1
balanced
Atoms H
4
4
Atoms O
4
4
balanced
balanced
Chapter 6, Section 1
11
Guide to Balancing a Chemical
Equation
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Chapter 6, Section 1
12
Steps to Balancing a Chemical
Equation
Balance the following chemical reaction:
Ethanol (C2H6O) burns in the presence of oxygen
gas(O2) to produce steam (H2O) and carbon dioxide
(CO2) gas.
Step 1 Write an equation using the correct formulas
of the reactants and products.
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Chapter 6, Section 1
13
Steps to Balancing a Chemical
Equation
Step 2 Count the atoms of each element in the
reactants and products.
Reactants Products
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Atoms of C
2
1
not balanced
Atoms of H
6
2
Atoms of O
3
3
not balanced
balanced
Chapter 6, Section 1
14
Steps to Balancing a Chemical
Equation
Step 3 Use coefficients to balance each element.
Step 4 Check the final equation to confirm it is
balanced.
Create a balance sheet to count atoms of each element.
Reactants Products
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Atoms of C
2
2
Atoms of H
6
6
Atoms of O
7
7
Chapter 6, Section 1
balanced
balanced
balanced
15
Learning Check
Determine if each equation is balanced or not.
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Chapter 6, Section 1
16
Solution
Determine if each equation is balanced or not.
Reactants
Products
Atoms of Na
1
3
Atoms of N
2
1
not balanced
not balanced
Since different numbers of Na and N atoms are present
in the reactants and products, the equation is not
balanced.
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Chapter 6, Section 1
17
Solution
Determine if each equation is balanced or not.
Reactants
Products
Atoms of C
2
2
Atoms of H
6
6
Atoms of O
1
1
balanced
balanced
balanced
Since the same numbers of C, H and O atoms are
present in the reactants and products, the equation is
balanced.
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Chapter 6, Section 1
18
Learning Check
Write a balanced equation for the reaction of nitrogen gas
(N2) with hydrogen gas (H2) to form ammonia gas (NH3).
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Chapter 6, Section 1
19
Solution
Write a balanced equation for the reaction of nitrogen gas
(N2) with hydrogen gas (H2) to form ammonia gas (NH3).
Step 1 Write an equation using the correct formulas
of the reactants and products.
Step 2 Count the atoms of each element in the
reactants and products.
Reactants Products
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Atoms of N
2
1
not balanced
Atoms of H
2
3
not balanced
Chapter 6, Section 1
20
Solution
Write a balanced equation for the reaction of nitrogen gas
(N2) with hydrogen gas (H2) to form ammonia gas (NH3).
Step 3 Use coefficients to balance each element.
Step 4 Check the final equation to confirm it is
balanced.
Reactants Products
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Atoms of N
2
2
Atoms of H
6
6
Chapter 6, Section 1
balanced
balanced
21
Learning Check
Check the balance of atoms in the following equation:
1. number of H atoms in products
A. 2
B. 4
C. 8
2. number of O atoms in reactants
A. 2
B. 4
C. 8
3. number of Fe atoms in reactants
A. 1
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B. 3
Chapter 6, Section 1
C. 4
22
Solution
Check the balance of atoms in the following equation:
1. number of H atoms in products
C. 8 (4H2O)
2. number of O atoms in reactants
B. 4 (Fe3O4)
3. number of Fe atoms in reactants
B. 3 (Fe3O4)
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Chapter 6, Section 1
23
Equations with Polyatomic Ions
When balancing equations with polyatomic ions that
remain the same on both sides of the equation,
balance them as a unit.
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Chapter 6, Section 1
24
Balancing with Polyatomic Ions
Balance the following chemical equation.
Step 1 Write the equation using the correct formulas
of the reactants and products.
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Chapter 6, Section 1
25
Balancing with Polyatomic Ions
Balance the following chemical equation.
Step 2 Count the atoms of each element in the
reactants and products.
Reactants Products
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Atoms of Na
3
1
PO43− ions
1
2
Atoms of Mg 1
3
Atoms of Cl
1
2
Chapter 6, Section 1
not balanced
not balanced
not balanced
not balanced
26
Balancing with Polyatomic Ions
Balance the following chemical equation.
Step 3 Use coefficients to balance each element.
Step 4 Check the final equation to confirm it is
balanced.
Reactants Products
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Atoms of Na
6
6
PO43− ions
2
2
Atoms of Mg
3
3
Atoms of Cl
6
6
Chapter 6, Section 1
balanced
balanced
balanced
balanced
27
Learning Check
Balance and list the coefficients from reactants to products.
1. __Fe2O3(s) + __C(s)
A. 2, 3, 2,3
B. 2, 3, 4, 3
2. __Al(s) + __FeO(s)
A. 2, 3, 3, 1
__Fe(s) + __CO2(g)
__Fe(s) + __Al2O3(s)
B. 2, 1, 1, 1
3. __Al(s) + __H2SO4(aq)
A. 3, 2, 1, 2
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C. 1, 1, 2, 3
__Al2(SO4)3(aq) + __H2(g)
B. 2, 3, 1, 3
Chapter 6, Section 1
C. 3, 3, 3, 1
C. 2, 3, 2, 3
28
Solution
Balance and list the coefficients from reactants to products.
2
3
1. __Fe
2O3(s) + __C(s)
4
3
__Fe(s)
+ __CO
2(g)
B. 2, 3, 4, 3
2
3
2. __Al(s)
+ __FeO(s)
3
1 2O3(s)
__Fe(s)
+ __Al
A. 2, 3, 3, 1
3. __Al(s)
+ __H
2
3 2SO4(aq)
__Al
1 2(SO4)3(aq) + __H
3 2(g)
B. 2, 3, 1, 3
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Chapter 6, Section 1
29