Types of Chemical Reactions

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Types of Chemical Reactions
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Chemical Reactions
If you add two substances together sometimes you
get a chemical reaction. This is when a new
substance is made. It is very difficult to
reverse the reaction and get the original
substances back. Signs that a chemical reaction
has taken place include a change in colour, heat
being given off or bubbles of gas being made.
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Adding acid to alkali
Fireworks
Driving a car
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?
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Boiling the kettle
frying an egg
Ice cream melting
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x
x
Dissolving sugar in tea
Discuss in pairs which of these are chemical
reactions
Burning a candle
Melting candle wax
The changes that are not chemical changes are
called physical changes
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x
x
Lighting a match
Making ice cubes
Ironing clothes
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x
x
Launching a space rocket
Printing
Baking a cake
x
?
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Objectives

• Define and give general equations for synthesis,
  decomposition, single-replacement, and
  double-replacement reactions.
• Classify a reaction as synthesis, decomposition,
  single-replacement, single-replacement,
  double-replacement, or combustion.

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Objectives

• List three types of synthesis reactions and six
  types of decomposition reactions.
• List four types of single-replacement reactions
  and three types of double-replacement reactions.
• Predict the products of single reactions given
  the reactants.

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Background

• Thousands of known chemical reactions occur in
  various systems. Memorizing the equations for so
  many chemical reactions would be difficult. It is
  more useful and realistic to classify reactions
  according to various similarities and
  regularities.

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The 5 Types of Reactions
Combustion
Decomposition
Double Replacement
Single Replacement
Synthesis
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Synthesis Reactions

• In a synthesis reaction, also known as
  composition reaction, two or more substances
  combine to form a new compound.
• General equation A X AX.
• Types of synthesis reactions
• Reactions of elements with oxygen and sulfur.
• Reactions of metals with halogens.
• Synthesis reaction with oxides.

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Synthesis Reaction
Synthesis reaction 2 substances combine to form
a single product A B ? AB

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2Mg(s) O2(g)? 2MgO(s) Magnesium and oxygen
combine to form magnesium oxide. 2H2(g) O2(g)?
2H2O(l) Hydrogen and oxygen combine to form
dihydrogen monoxide
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Look at the reactants represented below, which
reaction involves elements as reactants? Which
reaction involves compounds as reactants?

• Synthesis reaction

• Decomposition reaction

A synthesis reaction involves the combination
smaller molecules
A decomposition reaction involves the breaking
apart of larger molecules
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Lets us look at two of the reaction
typessynthesis and decomposition

• Recognizing the types of reactants is key to
  identifying the reaction type

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Synthesis Reactions

• Involve the combination of smaller atoms and /or
  molecules into larger molecules.
• They are also called combination reactions

• General formula
• A B AB
• If you see two elements as reactants, you know
  the reaction has to be a sysnthesis reaction

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• Synthesis reactions can also involve combinations
  of small molecules.
• For example, when ammonia and hydrogen chloride
  vapours combine, they form a white smoke as solid
  particles of ammonium chloride are formed.
• Hydrogen chloride ammonia ammonium
  chloride
• HCl NH3 NH4Cl

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Typical example , rainwater

• Similarly, combination of water and carbon
  dioxide molecules Synthesis reaction
• CO2 H2O H2CO3(aq)

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• Examples of Reaction of Elements with Oxygen and
  Sulfur
• Forming Oxides and sulfides
• 2Mg(s) O2(g) 2MgO(s)
• 16Rb(s) S8(s) 8Rb2S(s)
• 8Ba(s) S8(s) 8BaS(s)
• S8(s) 8O2(g) 8SO2(g)
• C(s) O2(g) CO2(g)
• 2C(s) O2(g) CO(g)
• 2H2(g) O2(g) 2H2O(l)

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• Forming Oxides and sulfides
• 2Fe(s) O2(g) 2FeO(s)
• 4Fe(s) 3O2(g) 2Fe2O3(s)

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• Reactions of Metals with Halogens (most metals
  react with the halogens (group 17) to form either
  ionic or covalent compounds.
• Group 1 metals with Group 17 elements
• 2Na(s) Cl2(g) 2NaCl(s)
• 2K(s) I2(g) 2KI(s)
• Group 2 metals with Group 17 elements
• Mg(s) F2(g) MgF2(s)
• Sr(s) Br2(l) SrBr2(s)

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• Fluorine is so reactive that it combines with
  almost all metals
• 2Na(s) F2(g) 2NaF(s)
• 2Co(s) F2(g) 2CoF3(s)
• U(s) 3F2(g) UF6(g)
• Practical application with fluorine
• Sodium fluorine added to municipal water
  supplies.
• Cobalt(III) fluoride is a strong fluorinating
  agent.
• Uranium(VI) fluoride is the first step in the
  production of uranium for use in nuclear power
  plants.

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• Synthesis Reactions with Oxides
• Oxides of active metals react with water to
  produce metal hydroxides - example
• CaO(s) H2O(l) Ca(OH)2(s)
• Many oxides of nonmetals (upper right portion of
  the periodic table) react with water to produce
  oxyacids - example
• SO2(g) H2O(l) H2SO3(aq)
• this reacts with oxygen to produce sulfuric acid
• 2H2SO3(aq) O2(g) 2H2SO4(aq)
• Certain metal oxides and nonmetal oxides react
  with each other in synthesis reaction to form
  salts. CaO(s) SO2(g) CaSO3(s)

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Decomposition Reactions

• In a decomposition reaction, a single compound
  undergoes a reaction the produces two or more
  products.
• General equation AX A X

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Decomposition Reactions

• It involve the splitting of a large molecule into
  elements or smaller molecules.
• General formula
• AB A B

• Example, electrolysis of water uses electricity
  to split water molecules into their elements
• water hydrogen oxygen
• H2O H2 O2
• 2H2O 2H2 O2

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Decomposition Reaction

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

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2H2O2(aq)? O2(g) 2H2O(l) Hydrogen peroxide
decomposes into oxygen gas and dihydrogen
monoxide. 2NaCl(s) ? 2Na(s) Cl2(g) Sodium
chloride decomposes into sodium and chlorine gas.
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• Types of decomposition reactions
• Decomposition of Binary Compounds
• Decomposition of Metal Carbonates
• Decomposition of Metal Hydroxides
• Decomposition of Metal Chlorates
• Decomposition of Acids
• Decomposition of Binary Compounds
• electricity
• 2H2O(l) 2H2(g) O2(g) (called electrolysis)
• 2HgO(s) 2Hg(l) O2(g)

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• Decomposition of Metal Carbonates
• CaCO3(s) CaO(s) CO2(g)
• Decomposition of Metal Hydroxides
• Ca(OH)2(s) CaO(s) H2O(g)
• Decomposition of Metal Chlorates
• 2KClO3(s) 2KCl(s) 3O2(g)
• Decomposition of Acids
• H2CO3(aq) CO2(g) H2O(l)
• H2SO4(aq) SO3(g) H2O(l)

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Single-Replacement Reactions

• In a single-replacement reaction, also know as a
  displacement reaction, one element replaces a
  similar element in a compound.
• A BX AX B or
• Y BX BY X

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Single Displacement Reactions

• Are chemical changes that involve an element and
  a compound as reactants.
• One element displaces or replaces another element
  from the compound.
• Example, when magnesium ribbon is placed in a
  solution of silver nitrate

• Mg AgNo3 Ag Mg(NO3)2
• Mg 2AgNO3 2Ag Mg(NO3)2

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Single Replacement Reaction

• Single Replacement reaction A single element
  takes the place of another element in a compound.
• A BC ? C AB

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AgNO3(aq) Cu(s) ? Ag(s) CuNO3(aq) Copper
replaces silver in silver nitrate to copper (I)
nitrate and silver. Zn(s) 2HCl(aq) ? H2(g)
ZnCl2(aq) Zinc replaces hydrogen in hydrogen
chloride to yield hydrogen gas and zinc chloride.
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• Types of single-replacement reactions
• Replacement of a Metal in a Compound by Another
  Metal
• Replacement of Hydrogen in Water by a Metal
• Replacement of Hydrogen in Acid by a Metal
• Replacement of Halogens
• Replacement of a Metal in a Compound by Another
  Metal.
• A more active metal will replace a less active
  metal.
• 2Al(s) 3Pb(NO3)2(aq) 3Pb(s) 2Al(NO3)3(aq)

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• Replacement of Hydrogen in Water by a Metal
• The most-active metals such as those in Group 1,
  react vigorously with water to produce metal
  hydroxides and hydrogen.
• example 2Na(s) 2H2O(l) 2NaOH(aq) 4H2(g)
• example 3Fe(s) 4H2O(g) Fe3O4(s) 4H2(g)
  (Less-active metals react with steam to form a
  metal oxide and hydrogen gas)
• Replacement of Hydrogen in an Acid by a Metal
• The more-active metals react with certain acidic
  solutions replacing the hydrogen in the acid.
• example Mg(s) 2HCl(aq) H2(g) MgCl2(ag)

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• Replacement of Halogens
• One halogen replaces another halogen in a
  compound. Fluorine is the most-active halogen and
  can replace any other halogen in their compounds.
• Cl2(g) 2KBr(aq) 2KCl(aq) Br2(l)
• F2(g) 2NaCl(aq) 2NaF(aq) Cl2(s)

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Double-Replacement Reactions

• In double-replacement reactions, the ions of two
  compounds exchange places in an aqueous solution
  to form two new compounds.
• General equation AX BY AY BX
• Formation of a Precipitate
• The formation of a precipitate occurs when the
  cations of one reactant combine with the anions
  of another reactant to form an insoluble or
  slightly soluble compound.
• 2KI(aq) Pb(NO3)2(aq) PbI2(s) 2KNO3(aq)

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• Formation of a Gas
• In some double-replacement reactions, one of the
  products in an insoluble gas that bubbles out of
  the mixture.
• FeS(s) 2HCl(aq) H2S(g) FeCl2(aq)
• Formation of Water
• In some double-replacement reactions, a very
  stable molecular compound, such as water, is one
  of the products.
• HCl(aq) NaOH(aq) NaCl(aq) H2O(l)

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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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HCl(aq) NaOH(aq) ? HOH(l) NaCl(aq) Hydroxide
and chlorine switch places to hydrogen hydroxide
(water) and sodium chloride Na2S(aq)
Zn(NO3)2(aq) ? 2NaNO3(aq) ZnS (s) Sulfur and
nitrate switch places to form sodium nitrate and
zinc sulfide.
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Combustion Reactions

• In a combustion reaction, a substance combines
  with oxygen, releasing a large amount of energy
  in the form of light and heat.
• 2H2(g) O2(g) 2H2O(g)
• C3H8(g) 5O2(g) 3CO2(g) 4H2O(g)

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Combustion Reaction

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

CH4(g) 2O2(g) ? 2H2O (l) CO2(g) Methane burns
in oxygen to produce water and carbon
dioxide. C12H22O11(s) 12O2(g) ? 11H2O(l)
12CO2(g) Sucrose burns in oxygen to produce water
and carbon dioxide.
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Section Review

• List five types of chemical reactions.
• Complete and balance each of the following
  reactions identified by type
• synthesis ______ Li2O
• decomposition Mg(ClO3)2 ______
• single-replacement Na H2O ______
• double-replacement HNO3 Ca(OH)2
• combustion C5H12 O2 ______

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Section Review

• Classify each of the following reactions
• N2(g) 3H2(g) 2NH3(g)
• 2Li(s) 2H2O(l) 2LiOH(aq) H2(g)
• 2NaNO3(s) 2NaNO2(s) O2(g)
• 2C6H14(l) 19O2(g) 12CO2(g) 14H2O(l)
• NH4Cl(s) NH3(g) HCl(g)
• BaO(s) H2O(l) Ba(OH)2(aq)
• AgNO3(aq) NaCl(aq) AgCl(s) NaNO3(aq)