Chemical Reactions

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Chemical Reactions
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Quick Review
Matter is the stuff that makes up the universe.
mass
volume
All matter has ______ and ________.
All matter is composed of basic building
blocks known as _______.
atoms
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Quick Review
We know that matter can undergo changes both
_________ and __________.
physical
chemical
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Quick Review
When matter undergoes a physical change the
composition of the substance is unchanged.

• When matter undergoes a chemical change or
  reaction the composition of the substance is
  changed and chemical bonds are formed.

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What happens during a chemical reaction?

• Atoms in the reactants are rearranged to form one
  or more different substances (products).
• Old bonds are broken new bonds form.
• Reactants Products
• MgO C CO Mg

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How do you know a chemical reaction has occurred?

• Evolution of heat and light
• Formation of a gas
• Formation of a precipitate (formation of a solid
  in a solution)
• Color change
• Temperature changes (endothermic/exothermic)
• A new odor is produced

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Learning Check 1

• Classify each of the following as a
• 1) physical change or 2) chemical change
• A. ____ a burning candle
• B. ____ melting ice
• C. ____ toasting a marshmallow
• D. ____ cutting a pizza
• E. ____ polishing silver

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Solution 1

• Classify each of the following as a
• 1) physical change or 2) chemical change
• A. __2__ a burning candle
• B. __1_ melting ice
• C. __2__ toasting a marshmallow
• D. __1__ cutting a pizza
• E. __2__ polishing silver

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A Chemical Reaction

• Reactants Products

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Learning Check 2

• A. How does an equation indicate a change in
• the identity of the reacting substances?
• B. How did the black and white reactants
• combine?
• C. Did all the reactants form product? Why or
• why not?

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Solution 2

• A. How does an equation indicate a change in the
  identity of
• the reacting substances?
• The formulas of the reactants are different than
  the formulas of the products.
• B. How did the black and white reactants
  combine?
• 1 black combined with 1 white.
• C. Did all the reactants form product? Why or
  why not?
• No. There were more black reactants than
  white.

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How do we represent these chemical reactions?

• Chemists use statements called equations.
• Chemical equations do not express numerical
  equalities as in math.
• Chemical equations show the direction in which
  the reaction progresses. Instead of an equal sign
  (), an arrow is used
• (means yield)

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Word Equations

• A statement using words to describe a chemical
  reaction.
• Sodium (s) Chlorine (g) Sodium
  Chloride (s)
• The statement reads sodium and chlorine react to
  produce or yield
• sodium chloride.
• Useful but lacks important information

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Chemical Symbols
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Skeletal Equation

• Uses chemical formulas instead of words to
  identify reactants and products.
• Important step in writing a complete equation
• Na(s) Cl2(g) NaCl(s)

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Learning Check 4

• Write skeleton equations for the following word
  equations.
• hydrogen(g) bromine(g) hydrogen
  bromide(g)

carbon(s) sulfur(s) carbon
disulfide(s)
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Solution 4

• Write skeleton equations for the following word
  equations.
• hydrogen(g) bromine(g) hydrogen
  bromide(g)
• H2(g) Br2(g) HBr(g)

carbon(s) sulfur(s) carbon
disulfide(s) C(s) S(s) CS2(s)
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Writing a Chemical Equation

• Chemical symbols give a before-and-after
  picture of a chemical reaction
• Reactants Products
• MgO C CO Mg
• magnesium oxide to form carbon monoxide
• reacts with carbon and
  magnesium

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Types of Reactions

• There are six types of chemical reactions we will
  talk about
• Synthesis reactions
• Decomposition reactions
• Single displacement reactions
• Double displacement reactions
• Combustion reactions
• You need to be able to identify the type of
  reaction

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1. Synthesis reactions

• Synthesis reactions occur when two substances
  (generally elements) combine and form a compound.
  (Sometimes these are called combination or
  addition reactions.)
• reactant reactant ? 1 product
• Basically A B ? AB
• Example 2H2 O2 ? 2H2O
• Example C O2 ? CO2

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Synthesis Reactions

• Here is another example of a synthesis reaction

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2. Decomposition Reactions

• Decomposition reactions occur when a compound
  breaks up into the elements or in a few to
  simpler compounds
• 1 Reactant ? Product Product
• In general AB ? A B
• Example 2 H2O ? 2H2 O2
• Example 2 HgO ? 2Hg O2

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Decomposition Reactions

• Another view of a decomposition reaction

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3. Single Replacement Reactions

• Single Replacement Reactions occur when one
  element replaces another in a compound.
• A metal can replace a metal () OR a nonmetal
  can replace a nonmetal (-).
• element compound? product product
• A BC ? AC B (if A is a metal) OR
• A BC ? BA C (if A is a nonmetal)
• (remember the cation always goes first!)

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Single Replacement Reactions

• Another view

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Single Replacement Reactions

• Sodium chloride solid reacts with fluorine gas
• NaCl(s) F2(g) ? NaF(s)
  Cl2(g)
• Note that fluorine replaces chlorine in the
  compound
• Aluminum metal reacts with aqueous copper (II)
  nitrate
• Al(s) Cu(NO3)2(aq)? Cu(s)
  Al(NO3)3(aq)

2
2
2
3
3
2
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4. Double Replacement Reactions

• Double Replacement Reactions occur when a metal
  replaces a metal in a compound and a nonmetal
  replaces a nonmetal in a compound
• Compound compound ? product product
• AB CD ? AD CB

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Double Replacement Reactions

• Think about it like foiling in algebra, first
  and last ions go together inside ions go
  together
• Example
• AgNO3(aq) NaCl(s) ? AgCl(s) NaNO3(aq)
• Another example
• K2SO4(aq) Ba(NO3)2(aq) ? KNO3(aq) BaSO4(s)

2
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5. Combustion Reactions

• Combustion reactions occur when a hydrocarbon
  reacts with oxygen gas.
• This is also called burning!!! In order to burn
  something you need the 3 things in the fire
  triangle1) A Fuel (hydrocarbon)2) Oxygen to
  burn it with3) Something to ignite the reaction
  (spark)

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Combustion Reactions

• In general CxHy O2 ? CO2 H2O
• Products in combustion are ALWAYS carbon dioxide
  and water. (although incomplete burning does
  cause some by-products like carbon monoxide)
• Combustion is used to heat homes and run
  automobiles (octane, as in gasoline, is C8H18)

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Combustion

• Example
• C5H12 O2 ? CO2 H2O
• Write the products and balance the following
  combustion reaction
• C10H22 O2 ?
  
  
  
  
  
  
  
  
  
  
  
  

5
8
6
11
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22
CO2 H2O
10
2
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6. Acid-base

• This is a special kind of double displacement
  reaction that takes place when an acid and base
  react with each other. The H ion in the acid
  reacts with the OH- ion in the base, causing the
  formation of water. Generally, the product of
  this reaction is some ionic salt and water
• HA BOH ---gt H2O BA
• One example of an acid-base reaction is the
  reaction of hydrobromic acid (HBr) with sodium
  hydroxide
• HBr NaOH ---gt NaBr H2O

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Mixed Practice

• State the type and balance the following
  reactions
• BaCl2 H2SO4 ?
• C6H12 O2 ?
• Zn CuSO4 ?
• Cs Br2 ?
• FeCO3 ?

BaSO4 HCl
2
6
6
CO2 H2O
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ZnSO4 Cu
CsBr
2
2
FeO CO2