Transcript Chapter 9

Chapter 8
Chemical reactions
Chemical Reaction
• Represents a chemical change
• Reactants
products
• When a chemical change occurs the
products have a different set of properties
than the reactants.
• Follows the Law of the Conservation of
Mass
Law of the conservation of mass
• Matter can not be destroyed or created it
can only be rearranged.
• Mass of the reactants must equal the mass
of the products.
• That is why all chemical reactions must be
balanced.
Balancing Equations
• Preliminaries- if a word problem, identify the
reactants and the products of the reaction.
• Write the equation in chemical reaction form
Generally stated as
A+B
C
• First do an atom count of the reactants and of the
products.
• Second – adjust coefficients to make the number
of atoms for each element equal on both sides.
Example
LiAlH4 + H2 O
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1- Li
1-Al
6-H
1- O
LiOH + Al(OH)3 + H2
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1 –Li
1- Al
6- H
4- O
Example
• Al(NO3)3 + NaOH
Al(OH)3 + NaNO3
Types of Chemical Equations
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Single displacement reactions
Double displacement reactions
Decomposition reactions
Synthesis reactions
Combustion reactions
Single and double displacement
• General form of a single displacement
reaction
Single Displacement
A+ BC
B + AC
(redox reactions)
Double displacement
AB + CD
AD + CB
Decomposition and Synthesis
• Decomposition reactions general formula
•
AB
A+B
• Synthesis reactions general formula
•
A+B
AB
Combustion reactions
• Will always follow the same patterntemplate
• A + O2
C4H8 + O2
C4H8 + 6O2
CO2 + H2O + Energy
CO2 + H2O + Energy
4CO2 +4H2O+Energy
Percent Yield
• Percent yield = actual amount of the
product/ the theoretical amount of the
product X 100.
• Until we do stoichiometry,the theoretical
amount will be given to you. Once we
completed 9.2, you will be able to find out
the theoretical amount yourself.
Example
• The actual amount in a reaction is 39.7 g,
the predicted amount was 65.6 grams. What
is the percent yield?
• (39.7g/ 65.6g ) x 100 =
• 60.5%
More on combustion equations
• Balance the equations
• Use the molar heat of combustion to find
the amount of heat evolved.
• Review terms exothermic
•
endothermic
Chemical reaction symbols
• Solid – cr
• Gas – g
• Liquid/ dissolved in water - aq