Chapter 6: Chemical Reactions

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Chapter 6 Chemical Reactions
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Chemical Equation

• represents a chemical change or reaction
• Reactants ? Products
• Reactants chemicals before the reaction
• Products substance formed in the reaction

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5 signs of a chemical reaction

• 1. Color Change

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5 signs of a chemical reaction

• 2. Precipitation of a Solid

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5 signs of a chemical reaction

• 3. Energy Change heat or light absorbed or
  released

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5 signs of a chemical reaction

• 4. Odor Changes

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5 signs of a chemical reaction

• 5. Gas Release

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• Reactions can be described several ways
• 1. In a sentence
• Copper reacts with chlorine to form copper (II)
  chloride.
• 2. In a word equation
• Copper chlorine copper (II) chloride
• Using formulas
• Cu Cl2 ? CuCl2

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Symbols used in Reactions
Symbol Explanation
Used to separate two reactants or two products
? Yields, separates reactants and products
(s), (l), (g) State of matter Fe (s)
(aq) Aqueous solution dissolved in water
Heat supplied to the rxn
Catalyst used (speeds up the rxn time)
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Assignment 7 Write the word equations below as
chemical equations and balance

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• 1. Zinc and lead (II) nitrate react to form zinc
  nitrate and lead.
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2. Aluminum bromide and chlorine gas react to
form aluminum chloride and bromine gas.
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Diatomic Elements
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3. Sodium phosphate and calcium chloride react
to form calcium phosphate and sodium chloride.
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In a chemical reaction

• Law of Conservation of Matter states that matter
  isnt created or destroyed.
• The way atoms are joined is changed

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Because of the LAW OF CONSERVATION OF MATTER, we
have to BALANCE EQUATIONS!!!
To BALANCE AN EQUATION means to make sure that
the NUMBER of atoms of each element is the same
in the reactants and in the products!
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Balancing Rules

• You may change the coefficients to any number you
  want, but
• You may NEVER change a subscript.
• A coefficient is a number written in front of the
  compound

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Balancing example 1

• C O ? CO2

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Balancing example 2

• Zn HCl ? H2 ZnCl2

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Balancing example 3

• CuO C ? Cu CO2

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Balancing example 4

• O3 ? O2

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Balancing example 5

• Al CuCl2 ? Cu AlCl3

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Balancing example 6

• C H2 ? C3H8

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Balancing example 7

• CF4 Br2 ? CBr4 F2

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Balancing example 8

• Hg2I2 O2 ? Hg2O I2

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Balancing example 9

• N2 H2 ? NH3

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Balancing example 10

• KClO3 ? KCl O2

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Balancing example 11

• H2 O2 ? H2O

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Balancing example 12

• AlBr3 K2SO4 ? KBr Al2(SO4)3

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5 Types of Chemical Reactions

1. Synthesis
2. Decomposition
3. Single Replacement (Displacement)
4. Double Replacement (Displacement)
5. Combustion

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Synthesis Reaction

• Synthesis reaction 2 substances are combined to
  form a single product
• A B ? AB

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Synthesis Examples

• 2Mg O2 ? 2MgO
• Magnesium and oxygen combine to form magnesium
  oxide.
• 2H2 O2 ? 2H2O
• Hydrogen and oxygen combine to form dihydrogen
  monoxide (water)

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Synthesis Demo

• Ignite magnesium

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Decomposition Reaction

• Decomposition reaction A single compound is
  broken down into 2 or more products.
• AB ? A B

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Decomposition Examples

• 2NaCl(s) ? 2Na(s) Cl2(g)
• Sodium chloride (table salt) decomposes into
  sodium and chlorine gas.
• CaCO3 ? CaO CO2
• Limestone (CaCO3 ) decomposes into lime (CaO) and
  carbon dioxide.

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Decomposition Demo

• Decomposition of Hydrogen Peroxide with MnO2 as a
  catalyst
• H2O2 ? O2 H2O

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Single Replacement Reaction

• Single Replacement reaction A single element
  takes the place of an element in a compound.
• A BC ? B AC

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Single Replacement Examples

• Mg BeO ? Be MgO
• Magnesium replaces beryllium in beryllium oxide
  to form magnesium oxide and beryllium.
• 2Na 2HCl ? H2 2NaCl
• Sodium replaces hydrogen in hydrochloric acid to
  yield hydrogen and sodium chloride.

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Single Replacement Demo

• Magnesium reacting with Hydrochloric acid
• Compared to Copper reacting with HCl

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Double Replacement Reaction

• Double Replacement reaction Elements in 2
  compounds switch places to form 2 new compounds.
• AB CD ? AD CB

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Double Replacement Examples

• MgO BeS ? MgS BeO
• Oxygen and sulfur switch places to form magnesium
  sulfide and beryllium oxide.
• Na2S Zn(NO3)2 ? 2Na(NO3) ZnS
• Sulfur and nitrate switch places to form sodium
  nitrate and zinc sulfide.

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Double Replacement Demo

• A double replacement between barium chloride and
  potassium sulfate
• Potassium Iodide and lead (II) nitrate produces
  potassium nitrate and lead (II) iodide

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Combustion Reaction

• Combustion reaction hydrocarbon (H and C) burn
  in oxygen to produce water and carbon dioxide.
  Heat is given off as energy.
• CxHy O2 ? H2O CO2

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Combustion Examples

• CH4 2O2 ? 2H2O CO2
• Methane burns in oxygen to produce water and
  carbon dioxide.
• C12H22O11 12O2 ? 11H2O 12CO2
• A sugar molecule burns in oxygen to produce water
  and carbon dioxide

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Combustion Demo

• Burn sugar
• Burn gasoline

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Factors that affect reaction rates

• Temperature
• Higher temperature faster reaction
• Concentration
• Changing the amounts of reactants
• High concentration means more particles per
  volume
• (3 H2O2 vs. 30 H2O2 )

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• Surface Area
• Reactions occur faster when there is more surface
  area
• Sugar cube vs. sugar packet dissolving
• Catalyst
• Used to speed up a reaction without being used up
  
• Enzymes are examples of catalyst

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Can you slow a reaction down?

• Inhibitor a substance added to slow reactions
  down
• Added to food products

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Limiting Reactant

• The reactant that is used up first
• Making a bicycle requires
• 1 frame 2 wheels ? 1 bicycle
• If you have 100 frames and 120 wheels, how
• many bicycles can you manufacture?
• What is the limiting reactant?

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