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Chapter 8
Chemical Equations and Reactions
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Section 8.1
Objectives:
• List 3 observations that suggest that a
chemical reaction has taken place.
• List 3 requirements for a correctly written
chemical reaction.
• Balance a formula equation by inspection.
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Chemical vs Physical Change
• Physical change – a change in substance that
does not change its chemical composition;
ex: phase changes, size changes
• Chemical change – a change in substance that
results in entirely new substance with different
chemical composition and properties;
ex: burning, tarnishing, rusting, baking
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Chemical Reactions
• A chemical reaction is a process by which substances
are changed into different substances (chemical
change).
• Chemical reactions DO NOT destroy or change actual
atoms, but they do break and rearrange bonds
between atoms often combining them into different
compounds or freeing atoms to be in a pure state.
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Indicators of a Chemical Reaction
1. Evolution of heat and/or light
2. Evolution of a gas (bubbles)
3. Formation of a precipitate
Precipitate = a solid that is formed as a
result of a chemical reaction in a solution
Sometimes, Colors change (not a positive
indication of a chemical reaction)
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Indicators of a Chemical Reaction
1. Change in temperature (drop in temperatureor
evolution of heat) and/or production of light
2. Evolution of a gas (bubbles)
3. Formation of a precipitate
Precipitate = a solid that is formed as a
result of a chemical reaction in a solution
Elephant toothpaste
Sometimes, Colors change indicates a reaction – but
not always. Be careful what is actually changing color.
If acid/base indicator, may not be a chemical reaction.
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• Cold and Hot Packs - Chemical Reactions
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• Chemical reactions are described by chemical
equations - a written representation of a
chemical reaction.
6H2O + 6CO2  C6H12O6 + 6O2
• The original substances are called reactants.
• The resulting substances are called products.
Reactants  Products
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Symbols used in
chemical equations
• +
• 
means “and” or “reacts with”
means “yields” or “produces” or
“breaks down into” or “decomposes”
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More Symbols used in chemical
equations:
•
•
•
•
•
(s) solid
(l) liquid
(g) gas
(aq) aqueous = dissolved in water
Heat or Δ
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Requirements for chemical equation:
1. Must include all reactants and products
2. Must contain correct formulas
AND…..
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3. Must satisfy Law of Conservation of Mass – mass
(atoms) cannot be created or destroyed in ordinary
chemical and physical changes
- same number of atoms of each element must be
on each side of equation
Equation must be balanced – done with
coefficients, whole numbers in front of formulas.
6CO2 + 6H2O  C6H12O6 + 6O2
Coefficients represent the relative number of
MOLES of that substance. If there is no coefficient it is assumed to be “1”.
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How do you balance a chemical
equation?
Na2O + H2O  NaOH
Only by adding coefficients.
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NEVER CHANGE A FORMULA!
H2O
H2O2
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Assignment
Using coefficients, balance the
assigned equations on handout
page 61.
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Writing correct equations from
sentences.
1st – identify reactants and products
2nd – write correct formulas for each
reactant and product
3rd – add symbols for physical states, + and yield,
catalysts, etc.
4th – balance with coefficients
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Remember diatomic elements!
• 7 diatomic elements
• Always found as diatomic if alone in an
equation.
• H2, N2, O2, F2, Cl2, Br2, I2
• Sulfur should be written as S8
• Phosphorus should be written as P4
• When pure – do not include prefixes in
name!!!
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Iron reacts with water and oxygen in air to yield iron III oxide.
1st – identify reactants and products and write word equation
with symbols for + and 
2nd – write formula equation with correct formulas
3rd – add symbols for physical states, catalysts, etc.
4th – balance with coefficients
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Write formula equation
Solid sulfur reacts with oxygen gas to produce gaseous sulfur trioxide.
1st – identify reactants and products and write word equation
with symbols for + and 
2nd – write formula equation with correct formulas
3rd – add symbols for physical states, catalysts, etc.
4th – balance with coefficients
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Dicarbon hexoxide reacts with oxygen to produce
carbon dioxide and water.
1st – identify reactants and products and write word equation
with symbols for + and 
2nd – write formula equation with correct formulas
3rd – add symbols for physical states, catalysts, etc.
4th – balance with coefficients
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Potassium chloride and phosphoric acid are produced
when potassium phosphate reacts with hydrochloric acid.
1st – identify reactants and products and write word equation
with symbols for + and 
2nd – write formula equation with correct formulas
3rd – add symbols for physical states, catalysts, etc.
4th – balance with coefficients
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Assignment
Complete Handout page 62 – Word Equations.
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Section 8.2
Objectives:
• Define synthesis, decomposition, single-replacement, and
double-replacement reactions.
• Classify a reaction as synthesis, decomposition, singlereplacement, and double-replacement, or combustion.
• Predict the products of simple reactions given the reactants.
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Types of Chemical Reactions
1.
2.
3.
4.
5.
Synthesis
A + X  AX
Decomposition
AX  A + X
Single-Replacement
A + BX  AX + B
Double-Replacement AX + BY  AY + BX
Combustion
CH4 + O2 CO2 + H2O
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Synthesis
A + X  AX
• Produces one product
• Examples:
• 2Fe + O2  2FeO
• S8 + 8O2  8SO2
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Decomposition
AX  A + X
• One compound in the reactant side of
equation.
• Examples:
•
•
•
•
•
2H2O  2H2 + O2
CaCO3  CaO + CO2
Ca(OH)2  CaO + H2O
2KClO3  2KCl + 3O2
H2SO4  SO3 + H2O
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Single-Replacement
A + BX  AX + B
•
•
•
•
Also called a single-displacement
Elements replace “like” elements (+ + - -)
A + BX  AX + B
or
Y + BX  BY + X
Remember if hydrogen in water is being
replaced that water is HOH.
2Na + 2H2O  2NaOH + H2
2Na + 2HOH  2NaOH + H2
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Double-Replacement
AX + BY  AY + BX
• Also called a double-displacement
• compound + compound 
compound + compound
• HCl + NaOH  NaCl + HOH
• Mg(NO3) + K3PO4  Mg3(PO4)2 + KNO3
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Combustion
• When a substance combines with oxygen and
burns to produce carbon dioxide and water.
• Hydrocarbons C3H8 + 5O2  3CO2 + 4H2O
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On handout, write the type of
reaction and, where indicated,
write the balanced equation.
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Knowing the type of reaction, you
can predict products.
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Predict product(s) and write the balanced
chemical equation.
Single replacement reaction between
magnesium bromide and chlorine
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Predict product(s) and write the balanced
chemical equation.
Single replacement reaction between aluminum and
iron (III) oxide
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Predict product(s) and write the balanced
chemical equation.
Double replacement reaction between silver I nitrate
and zinc I chloride
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Predict product(s) and write the balanced
chemical equation.
Double replacement reaction between sulfuric acid and
sodium hydroxide
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Predict product(s) and write the balanced
chemical equation.
Decomposition of HgO into mercury and oxygen
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Predict product(s) and write the balanced
chemical equation.
Synthesis of carbon dioxide from carbon monoxide and
oxygen.
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Activity Series
• Silently read page 271-272
• Write yourself an explanation of how to use
the activity series chart.
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What will be the products?
• NaCl + F2 
• FeCl3 + NaOH 
• Ag2O 
• AlBr3 + K2SO4 
• C8H18 + O2 
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Use the Activity Series to predict the products of these
possible reactions
• Ni + AgNO3 
• Ca + HCl 
• Ag + HCl 
• Br2 + NaI 
• I2 + NaBr 
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