Chapter 8
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Describing Chemical Change
Types of Chemical Reactions
Reactions in Aqueous Solution
Chapter 8.1
Describing Chemical Change
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Word Equations
Chemical Equations
Balancing Chemical Equations
Word Equations
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Reaction – one or more substances (the
reactants) change into one or more new
substances(the products)
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Reactants  Products
=?
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Yields, gives or reacts
Word Equations
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As reactants are converted to products,
the bonds holding the atoms together are
broken and new bonds are formed.
REMEMBER: The atoms are neither
created nor destroyed, just rearranged.
(Law of Conservation of Mass)
Word Equations
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Rust
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Iron reacts with oxygen to produce iron(III)
oxide (rust)
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Iron + Oxygen 
Iron(III) Oxide
(reactants) (yields) (products)
Word Equations
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Hydrogen peroxide reacts to form water
and oxygen gas.
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Hydrogen peroxide  water + oxygen
MnO2
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H2O2(aq)

H2O(l) + O2(g)
Word Equations
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Burning of Methane
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Methane + Oxygen  Carbon Dioxide + Water
Chemical Equations
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Iron + Oxygen
Iron(III) Oxide
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Fe + O2  Fe2O3
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Now add physical states
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Fe(s) + O2 (g)  Fe2O3 (s)
Chemical Equations
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Reactions with a catalyst
Catalyst – a substance that speeds up the
rate of a chemical reaction, but is not used
up in the reaction.
A catalyst is written above the arrow
Chemical Equations
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Manganese(IV) oxide catalyzes the
decomposition of hydrogen peroxide.
Balancing Chemical Reactions
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Each side of the equation has the same
number of atoms of each element.
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C(s) + O2(g)
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1 carbon, 2 oxygen  1 carbon, 2 oxygen

CO 2(g)
Balancing Chemical Reactions
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H2(g) + O2(g)
H2O(l)
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2 hydrogen, 2 oxygen  2 hydrogen, 1 oxygen
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Balance
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2 H2(g) + O2(g)

2 H2O(l)
Balancing Chemical Reactions
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Rules
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1) Determine the correct formulas
2) Write the formulas for the reactants on the
left and the products on the right. Place a 
in between. If there are two or more reactants
or products, use a + in between.
3) Count the number of atoms of each
element.
Balancing Chemical Reactions
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Rules
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4) Balance the elements one at a time until
you have equal numbers of elements on each
side
5) Make sure all numbers are in their smallest
whole number ratio.
Chapter 8.2 Types of Chemical
Reactions
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Classifying Reactions
Combination Reactions
Decomposition Reactions
Single-Replacement Reactions
Double-Replacement Reactions
Combustion Reactions
Predicting Products of Reactions
Classifying Reactions
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Identify the five general types or reactions:
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Combination Reactions
Decomposition Reactions
Single-Replacement Reactions
Double-Replacement Reactions
Combustion Reactions
Combination Reactions
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Two or more substance combine to form a
single substance.
General Reaction:
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R + S = RS
Example:
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2Mg(s) + O2(g)  2 MgO(s)
Decomposition Reactions
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A single compound is broken down into
two or more substances.
General Reaction:
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RS = R + S
Example:
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2HgO(s)  2 Hg(l) + O2(g)
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Single-Replacement Reactions
(Single Displacement Reactions)
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One element replaces a second element
in a compound.
General Reaction:
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T + RS = TS + R
Example:
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2K(s) + 2H2O(l)  2KOH(aq) + H2(g)
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http://www.kentchemistry.com/links/Kinetic
s/PredictingSR.htm
Double-Replacement Reactions
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Exchange of positive ions between two
reacting compounds.
General Reaction:
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RS + TU = RU + TS
R+S- + T+U- = R+U- + T+S-
Example:
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K2CO3(aq) + BaCl2(aq)  2KCl(aq) + BaCO3(s)
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http://www.kentchemistry.com/links/Kinetic
s/DRFlash.htm
Combustion Reactions
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An element or compound reacts with
oxygen often producing energy as heat or
light.
General Reaction:
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CxHy + (x + y/4) O2  xCO2 + (y/2)H2O
Example:
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CH4 (g) + 2O2 (g)  CO2(g) + 2H2O (g)
Name each type of reaction
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1) 2Mg(s) + O2(g)  2 MgO(s)
2) 2HgO(s)  2 Hg(l) + O2(g)
3) CH4 (g) + 2O2 (g)  CO2(g) + 2H2O (g)
4) 2K(s) + 2H2O(l)  2KOH(aq) + H2(g)
5) K2CO3(aq) + BaCl2(aq)  2KCl(aq) + BaCO3(s)
Name each type of reaction
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1) 2Mg(s) + O2(g)  2 MgO(s)
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2) 2HgO(s)  2 Hg(l) + O2(g)
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Combustion
4) 2K(s) + 2H2O(l)  2KOH(aq) + H2(g)
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Decomposition
3) CH4 (g) + 2O2 (g)  CO2(g) + 2H2O (g)
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Combination
Single Replacement
5) K2CO3(aq) + BaCl2(aq)  2KCl(aq) + BaCO3(s)
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Double Replacement
Chapter 8.3 Reactions in
Aqueous (aq) Solutions
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Net Ionic Equations
Predicting the Formation of a Precipitate
Net Ionic Equations
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AgNO3(aq) + NaCl (aq)  AgCl(s) + NaNO3 (aq)
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Double Replacement Reaction
Most ionic compounds dissociate (separate) into ions
(cations and anions) when they dissolve in water.
When all ions dissociate, we write the equation with
the charges on it. = Complete Ionic Equation
Complete Ionic Equation
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Ag+(aq) + NO3-(aq) + Na+(aq) Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)
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The equation can be simplified by crossing out any ions that do
not participate in the reaction. You do this by canceling out ions
that appear on both sides.
Ag+(aq) + NO3-(aq) + Na+(aq) Cl-(aq)  AgCl(s) + Na+(aq) + NO3-(aq)
You are left with the Net Ionic Equation:
Ag+(aq) + Cl-(aq)  AgCl(s)
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Pb(s) + AgNO3(aq)  Ag(s) + Pb(NO3)2(aq)
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Pb(s) + Ag+(aq) + NO3 -(aq)  Ag(s) + Pb2+(aq) + 2NO3-(aq)
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Pb(s) + Ag+(aq)  Ag(s) + Pb2+(aq)
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Need to balance charges
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Pb(s) + 2Ag+(aq)  2Ag(s) + Pb2+(aq)
Predicting the Formation of a
Precipitate
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Table F in reference table