chapter 5 chemical reactions physical change...
TRANSCRIPT
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Chapter 5 Chemical Reactions and Quantities
5.1 Chemical Changes
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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.
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Chemical Change
In a chemical change, n Reacting substances
form new substances with different compositions and properties.
n A chemical reaction takes place.
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Some Examples of Chemical and Physical Changes
TABLE 5.1
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Classify each of the following as a 1) physical change or 2) chemical change.
A. ____Burning a candle. B. ____Ice melting on the street.
C. ____Toasting a marshmallow. D. ____Cutting a pizza. E. ____Polishing a silver bowl.
Learning Check
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Classify each of the following as a 1) physical change or 2) chemical change. A. 2 Burning a candle. B. 1 Ice melting on the street. C. 2 Toasting a marshmallow. D. 1 Cutting a pizza. E. 2 Polishing a silver bowl.
Solution
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Chemical Reaction
In a chemical reaction, § A chemical change produces
one or more new substances. § There is a change in the
composition of one or more substances.
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Chemical Reaction
In a chemical reaction, § 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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Learning Check
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.
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Solution
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.
Heat and a flame B. Bleach removes stains from a shirt. Color change (color removed) C. Bubbles of CO2 are released when baking soda is mixed with vinegar.
Formation of gas (bubbles)
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Chapter 5 Chemical Reactions and Quantities
5.2 Chemical Equations
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Chemical Equations
A chemical equation § Gives the chemical formulas of the reactants on the left of the
arrow and the products on the right.
Reactants Product
C(s)
O2 (g) CO2 (g)
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Symbols Used in Equations
Symbols are used in chemical equations to show § The states of the reactants. § The states of the products.
§ The reaction conditions.
TABLE 5.2
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Chemical Equations are Balanced
In a balanced chemical reaction, § Atoms are not gained
or lost. § The number of atoms
in the reactants is equal to the number of atoms in the products.
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A Balanced Chemical Equation
In a balanced chemical equation, § 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 Al2S3 Not Balanced 2Al + 3S Al2S3 Balanced
2Al = 2Al 3S = 3S
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Learning Check
State the number of atoms of each element on the reactant side and the product side for each of the following balanced equations: A. P4(s) + 6Br2(l) → 4 PBr3(g)
B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
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Solution
A. P4(s) + 6Br2(l) → 4PBr3(g) 4 P 4 P
12 Br 12 Br B. 2Al(s) + Fe2O3(s) → 2Fe(s) + Al2O3(s)
2 Al 2 Al 2 Fe 2 Fe
3 O 3 O
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Learning Check
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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Solution
Determine if each equation is balanced or not. A. Na(s) + N2(g) → Na3N(s)
No. 2N on reactant side, 1N on product side. 1Na on reactant side, 3Na on product side.
Correctly balanced: 6Na(s) +N2(g) → 2Na3N(s) B. C2H4(g) + H2O(l) → C2H5OH(l)
Yes. 2C = 2C 6H = 6H 1O = 1O
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Equation for A Chemical Reaction
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Checking a Balanced Equation
Reactants Products 1 C atom = 1 C atom 4 H atoms = 4 H atoms 4 O atoms = 4 O atoms
Copyright © 2007 by Pearson Education, Inc. Publishing as Benjamin Cummings
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Guide to Balancing Equations
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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
STEP 4 Check that atoms of each element are equal in reactants and products. 4 N (4 x 1N) = 4 N (4 x 1N) 12 H (4 x 3H) = 12 H (6 x 2H) 10 O (5 x 2O) = 10 O (4O + 6O)
Balancing Chemical Equations
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Check the balance of atoms in the following: Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
A. Number of H atoms in products. 1) 2 2) 4 3) 8
B. Number of O atoms in reactants. 1) 2 2) 4 3) 8 C. Number of Fe atoms in reactants. 1) 1 2) 3 3) 4
Learning Check
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Fe3O4(s) + 4H2(g) 3Fe(s) + 4H2O(l)
A. Number of H atoms in products. 3) 8 (4H2O)
B. Number of O atoms in reactants. 2) 4 (Fe3O4)
C. Number of Fe atoms in reactants. 2) 3 (Fe3O4)
Solution
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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 2) 3, 1, 2 3) 3, 1, 1
B. __Al(s) + __Cl2(g) __AlCl3(s)
1) 3, 3, 2 2) 1, 3, 1 3) 2, 3, 2
Learning Check
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A. 3) 3, 1, 1
3Mg(s) + 1N2(g) 1Mg3N2(s)
B. 3) 2, 3, 2
2Al(s) + 3Cl2(g) 2AlCl3(s)
Solution
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Equations with Polyatomic Ions
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Balancing with Polyatomic Ions
Na3PO4(aq) + MgCl2(aq) NaCl(aq) + Mg3(PO4)2(s) Balance PO4
3- as a unit 2Na3PO4(aq) Mg3(PO4)2(s)
2PO43- = 2PO4
3- Balance Mg 3MgCl2(aq) Mg3(PO4)2(s)
3Mg2+ = 3Mg2+ Balance Na and Cl to complete balanced equation 3MgCl2(aq) + 2Na3PO4(aq) 6NaCl(aq) + Mg3(PO4)2(s)
6Na+ = 6Na+ 6Cl- = 6Cl-
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Balance and list the coefficients from reactants to products: A. __Fe2O3(s) + __C(s) __Fe(s) + __CO2(g)
1) 2, 3, 2,3 2) 2, 3, 4, 3 3) 1, 1, 2, 3 B. __Al(s) + __FeO(s) __Fe(s) + __Al2O3(s)
1) 2, 3, 3, 1 2) 2, 1, 1, 1 3) 3, 3, 3, 1 C. __Al(s) + __H2SO4(aq) __Al2(SO4)3(aq) + __H2(g)
1) 3, 2, 1, 2 2) 2, 3, 1, 3 3) 2, 3, 2, 3
Learning Check
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A. 2) 2, 3, 4, 3 2Fe2O3(s) + 3C(s) 4Fe(s) + 3CO2(g) B. 1) 2, 3, 3, 1 2Al(s) + 3FeO(s) 3Fe(s) + 1Al2O3(s)
C. 2) 2, 3, 1, 3 2Al(s) + 3H2SO4(aq) 1Al2(SO4)3(aq) + 3H2(g)
Solution