1. Synthesis Reactions

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1. Synthesis Reactions
Chapter 6 Chemical Reactions Occur in
Predictable Ways

• Occur when two or more reactants (usually
  elements) join to form a compound.
• General Formula
• A B ? AB
• (where A and B represent elements)

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can produce ionic or covalent compounds

• Ionic
• Magnesium metal reacts with oxygen
• gas to form magnesium oxide.
• 2Mg O2 ? 2MgO
• Covalent
• Nitrogen gas and oxygen gas join to form
  dinitrogen monoxide.
• 2N2 O2 ? 2N2O

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2. Decomposition

• are the opposite of synthesis reactions
• A compound breaks down into two or more products
  (often elements).
• General Formula
• AB ? A B
• (where A and B represent elements)

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Ionic and Covalent Compounds can Decompose

• Ionic
• Table salt, sodium chloride, can be broken down
  into sodium metal and chlorine gas by melting
  salt at 800ºC and running electricity through it.
• 2NaCl ? 2Na Cl2
• Covalent
• By running electricity through water,
• the water molecules decompose into
• hydrogen and oxygen gases.
• 2H2O ? 2H2 O2

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3. Single Replacement

• When one element from a compound is replaced with
  a separate element
• Two types, based on whether the single element is
  a metal or a non-metal
• General Forms
• A BC ? B AC where A is a metal, or
• A BC ? C BA where A is a non-metal

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The Two Types

• When A is a metal
• Aluminum foil in a solution of copper II chloride
  produces solid copper and aluminum chloride.
• Al CuCl2 ? Cu AlCl3
• When A is a non-metal
• When fluorine is bubbled through a sodium iodide
  solution, iodine and sodium fluoride are
  produced.
• F2 NaI ? I2 NaF

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4. Double Replacement

• elements swap places between two compounds to
  form two new compounds.
• Two ionic solutions react to form a precipitate
  (solid) and another ionic solution
• General Form
• AB CD ? AD CB

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4. Double Replacement Example

• potassium chromate and silver nitrate react to
  form a red precipitate, silver chromate, in a
  solution of potassium nitrate.
• K2CrO4(aq) AgNO3(aq) ? Ag2CrO4(s) KNO3(aq)

Note the K and Ag switch places in the compounds.
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5. Neutralization (aka Acid-Base reactions)

• occur when an acid and a base react to form a
  salt and water.
• acids (start with H)
• bases (end in OH, or begin with NH4)
• General Form
• Acid base ? salt water
• HX MOH ? MX H2O
• (where X and M are elements)

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5. Neutralization Examples

• Sulphuric acid is used to neutralize calcium
  hydroxide
• H2SO4 Ca(OH) 2 ? CaSO4 2H2O
• Phosphoric acid helps to neutralize the compounds
  that cause rust, such as iron (II) hydroxide.
• 2H3PO4 3Fe(OH)2 ? Fe3(PO4)2 6H2O

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6. Combustion

• occurs when a compound or element reacts with
  oxygen
• Always makes CO2 and H2O (in grade 10 examples)
• Aka. hydrocarbon combustion
• General Form
• CXHY O2 ? CO2 H2O

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6. Combustion Examples

• Natural gas (methane) is burned in furnaces to
  heat homes
• CH4 O2 ? CO2 2H2O
• An acetylene torch is used to weld metals
  together
• 2C2H2 5O2 ? 4CO2 2H2O
• Carbohydrates like glucose combine with oxygen in
  our body to release energy
• C6H12O6 6O2 ? 6CO2 6H2O

Take the Section 6.1 Quiz
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