Chemical Equations: Predicting Types of Reactions and Balancing

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Chemical Equations Predicting Types of Reactions
and Balancing
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I. Chemical Equations

• A chemical equation represents a chemical
  reaction
• Chemicals present before the reaction are shown
  to the left of the arrow and are called the
  REACTANTS.
• Chemical formed by the reaction are shown to the
  right of the arrow and are called the PRODUCTS.

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• REACTANTS ? PRODUCTS
• arrow indicates direction of change and is
  read as yields or produces

Example - CH4 2O2 ? CO2 2H2O
Reactants
Yield
Products
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II. Predicting Whether a Reaction Will Occur

• A. Four Driving Forces
• Formation of a solid (precipitate)
• Formation of water
• Transfer of electrons
• Formation of a gas
• B. If a driving force occurs the reaction will
  take place.

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III. Classifying Types of Reactions

• Double Displacement
• Single Displacement
• Decomposition
• Synthesis
• Combustion

AB YZ ? AZ YB
Reactants are 2 compounds
A YB ? Y AB
Reactants are 1 element 1 Compound
AB ? A B
Reactant is 1 compound
A B ? AB
Reactants are 2 elements or 2 oxides
CxHx O2 ? CO2 H2O
Reactants are hydrocarbon and oxygen
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Double Displacement reactions

• Precipitation Reaction Double Displacement
  reactions where the driving force is formation of
  a solid.
• Acid-Base/ Neutralization Reaction Double
  Displacement reactions where the driving force is
  formation of a liquid. (water)

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Oxidation Reduction reactions (redox)

• Driving Force Transfer of electron
• Always in single displacement reactions
• Sometimes in Synthesis and Decomposition
• Never in Double Displacement
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• Example

Anytime a single element is present a reaction is
also classified as redox
decomposition redox
synthesis redox
Zn(NO3)2(aq) 2 Na(s) ? 2NaNO3(aq) Zn(s)
single displacement redox
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Learning Check

• Classify the following reactions
• 2 KNO3 ? 2 KNO2 O2
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• 2 C2H2 5 O2 ? 4 CO2 2 H2O 
• CaO H2SO4 ? CaSO4 H2O
• 3 CaCl2 2 Na3PO4 ? Ca3(PO4)2(s) 6 NaCl
• 2 Fe 6 HC2H3O2 ? 2 Fe(C2H3O2)3 3 H2
• 2 KCl 3 O2? 2 KClO3

decomposition redox
combustion
Double displacement acid/base
Double displacement ppt
Single displacement redox
Synthesis redox
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Evidence of Chemical Reactions

• Four indicators a chemical reaction has occurred
• Color change - drastic
• Becomes Cloudy - Precipitate forms
• Bubbles - Gas forms
• Heat is produced or absorbed, or light

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• The reactants and the products contain the same
  atoms, but the chemical reaction has changed the
  way they are grouped.
• In a chemical reaction, atoms are neither created
  nor destroyed, all atoms present in the reactants
  must be present in some form in the products.
• There must be the same number of each type of
  atom on both sides of the equation.
• Balancing an equation makes sure that there is
  the same number and type of atom on both sides of
  the equation.

Law of Conservation
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• The chemical equation for a reaction provides us
  with three important pieces of information
• Identities of the reactants and products
• Relative numbers of each atom
• State of each reactant and product
• States of matter are shown with the following
  symbols
• (s) solid (l) liquid (g) gas
  (aq) aqueous, dissolved in water

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Balancing Chemical Equations

• Add coefficients to make sure you have the same
  number of each atom on either side of the
  equation.
• Identities of the compounds must never be changed
  when balancing. YOU CAN NEVER CHANGE A SUBSCRIPT
  IN A FORMULA!!!!!
• Most chemical equations can be balanced by trial
  and error.

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STEPS

• Write the unbalanced equation, making sure the
  formulas of the compounds are correct.
• Dont forget the diatomics BrINClHOF if they
  appear by themselves they must be written as Br2,
  I2, N2, Cl2, H2, O2, F2
• Use coefficients in front of each substance to
  balance. The coefficient, 1, is never written.
• The best balanced equation is the one with the
  smallest ratio of coefficients.
• DOUBLE CHECK YOUR WORK!!!!
• HINTS 1) Make odd numbers of atoms even.
• 2) Balance oxygen and hydrogen last.
• 3) If a polyatomic ion does not change count it
  as a group

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Examples

1. Reaction of hydrogen gas and oxygen gas to form
   liquid water.
2. Liquid ethanol, C2H5OH, reacts with oxygen gas to
   produce carbon dioxide gas and water vapor.

2 H2 (g) O2 (g) ? 2 H2O (l)
C3H5OH (g) 3 O2 (g) ? 2 CO2 (g) 3 H2O (g)
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• 3. Solid potassium reacts with liquid water to
  form hydrogen gas and potassium hydroxide that
  dissolves in water.
• LEARNING CHECK Nitrogen trihydride gas reacts
  with oxygen gas to produce nitrogen monoxide gas
  and water vapor.

2 K (s) 2 H2O (l) ? H2 (g) 2 KOH (aq)
4 NH3 (g) 5 O2 (g) ? 4 NO (g) 6 H2O (g)
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Examples

• C3H8(g) O2(g) ? CO2(g) H2O(g)
• NH4NO2(s) ? N2(g) H2O(g)
• NO(g) ? N2O(g) NO2(g)

C3H8(g) 5 O2(g) ? 3 CO2(g) 4 H2O(g)
NH4NO2(s) ? N2(g) 2 H2O(g)
3 NO(g) ? N2O(g) NO2(g)
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• LEARNING CHECK
• HNO3(aq) ? NO2(g) H2O(l) O2(g)
• Mg(s) H2O(l) ? Mg(OH)2(s) H2(g)

4 HNO3(aq) ? 4 NO2(g) 2 H2O(l) O2(g)
Mg(s) 2 H2O(l) ? Mg(OH)2(s) H2(g)
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Predicting States of Substances

• 1. Soluble solid readily dissolves in water
• 2. Insoluble and slightly soluble solid a
  solid where such a tiny amount dissolves in water
  that it is undetectable to the naked eye
• 3. Solubility is temperature dependent

State is aqueous - (aq)
State is solid - (s)
States of reactants can be manipulated
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Solubility Rules (on snoopy sheet)

• Ex. Predict whether the following substances are
  soluble or insoluble.

Solubility Rules Mainly water soluble (aq) All
nitrates are soluble. All acetates are
soluble. All chlorates are soluble. All chlorides
are soluble except AgCl, Hg2Cl2, and PbCl2 All
bromides are soluble except AgBr, Hg2Br2, PbBr2,
and HgBr2 All iodides are soluble except AgI,
Hg2I2, PbI2, and HgI2 All sulfates are soluble
except CaSO4, SrSO4, BaSO4, PbSO4, Hg2SO4, and
Ag2SO4 Mainly water insoluble (s) All sulfides
are insoluble except those of 1A and 2A elements
and (NH4)2S All carbonates are insoluble except
those of 1A and (NH4)2CO3 All phosphates are
insoluble except those of 1A and (NH4)3PO4 All
hydroxides are insoluble except those of 1A,
Ba(OH)2, Sr(OH)2 and Ca(OH)2
AgNO3
(aq)
Al(OH)3
(s)
ZnSO4
(aq)
Li2CO3
(aq)
Cu3PO4
(s)
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Learning Check

• Try these Determine if the following are AQUEOUS
  or SOLID
• 1. lead (II) nitrate
• 2. potassium sulfide
• 3. barium hydroxide
• 4. ammonium carbonate
• Turn to your neighbor and compare answers

solid
aqueous
aqueous
aqueous
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Special Rules

• 1. Acids are aqueous
• 2. Most metal oxides are solids
• 3. Most non-metal oxides are gases
• 4. Liquids Hg Br2
• Gases H2, N2, O2, F2, Cl2 and Noble Gases
  Solid all other elements
• 5. State (l) is reserved for pure liquids H2O,
  and some hydrocarbons

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Learning Check

• Determine the state
• 1. lead(II) phosphate
• 2. magnesium oxide
• 3. nickel
• 4. dinitrogen monoxide
• 5. chlorine
• 6. sulfuric acid
• 7. sodium sulfide

solid
solid
solid
gas
gas
aqueous
aqueous