Download chemical reaction and quantities

Chapter 5 Chemical Reactions
and Quantities
Physical Change
In a physical change,
§  The identity and
composition of the
substance do not
change.
§  The state can change,
or the material can be
torn into smaller
pieces.
5.1
Chemical Changes
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Some Examples of Chemical and
Physical Changes
Chemical Change
In a chemical change,
n  Reacting substances
form new substances
with different
compositions and
properties.
n  A chemical reaction
takes place.
TABLE 5.1
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
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Learning Check
Chemical Reaction
Classify each of the following as a
In a chemical reaction,
1) physical change or 2) chemical change.
§  A chemical change produces
one or more new substances.
A. ____Burning a candle.
§  There is a change in the
composition of one or more
substances.
B. ____Ice melting on the street.
C. ____Toasting a marshmallow.
D. ____Cutting a pizza.
E. ____Polishing a silver bowl.
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Chemical Reaction
Learning Check
In a chemical reaction,
Identify the visible evidence of a chemical reaction in
each of the following:
A. Methane gas in an outdoor heater burns with a blue
flame.
B. Bleach removes stains from a shirt.
C. Bubbles of CO2 are released when baking soda is
mixed with vinegar.
§  Old bonds are broken, and
new bonds are formed.
§  Atoms in the reactants are
rearranged to form one or
more different substances.
§  Fe and O2 form rust
(Fe2O3).
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Chapter 5 Chemical Reactions and
Quantities
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Chemical Equations
A chemical equation
5.2
Chemical Equations
§  Gives the chemical formulas of the reactants on the left of the
arrow and the products on the right.
Reactants
Product
O2 (g)
CO2 (g)
C(s)
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Symbols Used in Equations
Symbols are used in
chemical equations
to show
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Chemical Equations are Balanced
In a balanced
chemical reaction,
TABLE 5.2
§  Atoms are not gained
or lost.
§  The states of the reactants.
§  The number of atoms
in the reactants is
equal to the number of
atoms in the products.
§  The states of the products.
§  The reaction conditions.
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A Balanced Chemical Equation
Learning Check
In a balanced chemical equation,
State the number of atoms of each element on the
reactant side and the product side for each of the
following balanced equations:
§  There must be the same number of each type of atom on the
reactant side and on the product side.
§  Numbers called coefficients are used in front of one or more
formulas.
Al +
S
2Al + 3S
Al2S3
Not Balanced
Al2S3
Balanced
2Al
=
2Al
3S
=
3S
A. P4(s) + 6Br2(l) → 4 PBr3(g)
B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
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Learning Check
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Equation for A Chemical Reaction
Determine if each equation is balanced or not.
A. Na(s) + N2(g) → Na3N(s)
B. C2H4(g)
+ H2O(l) → C2H5OH(l)
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Checking a Balanced Equation
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Guide to Balancing Equations
Copyright © 2007 by Pearson Education, Inc.
Publishing as Benjamin Cummings
Reactants
1 C atom
4 H atoms
4 O atoms
=
=
=
Products
1 C atom
4 H atoms
4 O atoms
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Balancing Chemical Equations
Learning Check
STEP 1 Write the equation with the correct formulas.
NH3(g) + O2(g)
NO(g) + H2O(g)
STEP 2 Determine if the equation is balanced.
No, not all atoms are balanced.
STEP 3 Balance with coefficients in front of formulas.
4NH3 + 5O2
4NO + 6H2O
Check the balance of atoms in the following:
Fe3O4(s) + 4H2(g)
1) 2
1) 2
reactants and products.
=
=
=
2) 4
3) 8
B. Number of O atoms in reactants.
STEP 4 Check that atoms of each element are equal in
4 N (4 x 1N)
12 H (4 x 3H)
10 O (5 x 2O)
3Fe(s) + 4H2O(l)
A. Number of H atoms in products.
2) 4
3) 8
C. Number of Fe atoms in reactants.
4 N (4 x 1N)
12 H (6 x 2H)
10 O (4O + 6O)
1) 1
2) 3
3) 4
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Learning Check
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Equations with Polyatomic Ions
Balance each equation and list the coefficients in the balanced
equation going from reactants to products:
A. __Mg(s)
+ _N2(g)
__Mg3N2(s)
1) 1, 3, 2
B. __Al(s)
1) 3, 3, 2
2) 3, 1, 2
+ __Cl2(g)
3) 3, 1, 1
__AlCl3(s)
2) 1, 3, 1
3) 2, 3, 2
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Balancing with Polyatomic Ions
Na3PO4(aq) + MgCl2(aq)
Balance PO43- as a unit
2Na3PO4(aq)
2PO43Balance Mg
3MgCl2(aq)
3Mg2+
=
Learning Check
Balance and list the coefficients from reactants to products:
NaCl(aq) + Mg3(PO4)2(s)
=
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A. __Fe2O3(s) + __C(s)
Mg3(PO4)2(s)
2PO43-
1) 2, 3, 2,3
Mg3(PO4)2(s)
B. __Al(s) + __FeO(s)
3Mg2+
1) 2, 3, 3, 1
Balance Na and Cl to complete balanced equation
3MgCl2(aq) + 2Na3PO4(aq)
6NaCl(aq) + Mg3(PO4)2(s)
6Na+
=
6Na+
6Cl=
6Cl-
1) 3, 2, 1, 2 2) 2, 3, 1, 3
+ __CO2(g)
3) 1, 1, 2, 3
__Fe(s) +
2) 2, 1, 1, 1
C. __Al(s) + __H2SO4(aq)
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__Fe(s)
2) 2, 3, 4, 3
__Al2O3(s)
3) 3, 3, 3, 1
__Al2(SO4)3(aq) + __H2(g)
3) 2, 3, 2, 3
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