CHEMICAL REACTIONS AND EQUATIONS

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CHEMICAL REACTIONS AND EQUATIONS

• CHEMISTRY
• MS. WACK

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CHEMICAL REACTIONS

• In a chemical reaction, bonds are broken,
• atoms are rearranged, and new bonds are
• formed.
• Something new is produced.

H2 O2 ? H2O
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Is it a chemical reaction?
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Clues that a chemical reaction has occurred

• Odor
• Formation of a gas (may see bubbles)
• Precipitate formation
• Color Change (not always)
• New substances formed
• Energy is absorbed or released (not always)

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General Description of a Chemical Reaction
Reactants ? Products
The starting substances in a chemical reaction
The substances formed in a chemical reaction
Word Equations Use words and symbols to
represent chemical reactions.

• Uses words and symbols to describe a chemical
  reaction
• Common symbols used
• (s) solid (l) liquid (g) gas (aq)
  aqueousdissolved in water
• ? heat is added to the reaction reversible
  reaction
• a catalyst is added to the reaction

separates reactants or separates
products yields/produces
catalyst
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Word Equations

• Write the word equations for the following
• chemical reactions
• Hydrogen gas reacts with chlorine gas to produce
  hydrogen chloride, a gas with a sharp odor.
• Calcium oxide is produced when a piece of calcium
  is burned in oxygen.

HYDROGEN CHLORINE ? HYDROGEN CHLORIDE
CALCIUM OXYGEN ? CALCIUM OXIDE
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CHEMICAL EQUATIONS

• Formula Equations Use chemical formulas and
  symbols to represent a chemical reaction.
• Keys to writing formula equations
• Write the word equation firstthen, replace the
  words with chemical formulas.
• Make sure your formulas are correct!!!!!
• Make sure that each element in the reactants is
  also in the products and vice versa.
• The arrow must always go to the right.

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CHEMICAL EQUATIONS

• Write the formula equation for the
• reaction of calcium burning in oxygen to
• produce calcium oxide.

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LAW OF CONSERVATION OF MASS

• How does this law affect chemical equations?
• The mass of the reactants must equal the mass of
  the products
• The of atoms of each element must be equivalent
  on both sides of the reaction
• Chemical reactions must be balanced

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What are the s called?

• Mg2

superscript
2H2O ? 2H2 O2
coefficient
subscript
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BALANCING EQUATIONS

• Cd HCl ? CdCl2 H2

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BALANCING EQUATIONS

• MnSO4 ? MnO SO3

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BALANCING EQUATIONS

• H2SO4 NaOH ? Na2SO4 H2O

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BALANCING EQUATIONS

• Co O2 ? Co2O3

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BALANCING EQUATIONS

• Write a balanced chemical equation for the
• reaction in which magnesium reacts with nitrogen
• to produce magnesium nitride.

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BALANCING EQUATIONS

• Write a balanced chemical equation for the
  combustion of methane (CH4) in oxygen to produce
  carbon dioxide and water.

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BALANCING EQUATIONS

• Sodium phosphate is used to cut grease. Write a
  balanced equation for the reaction in which
  iron(II) chloride reacts with sodium phosphate to
  produce sodium chloride and iron(II) phosphate.

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BALANCING EQUATIONS

• Magnesium metal and water combine to form solid
  magnesium hydroxide and hydrogen gas.

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HEAT IN CHEMICAL REACTIONS

• Most chemical reactions involve changes in
  energy.
• The unit for energy is the Joule (J)
• This is because bond breaking requires energy and
  bond forming releases energy.
• Almost all chemical reactions either release or
  absorb energy
• This energy flow results in heat, either being
  absorbed or released.

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EXOTHERMIC REATIONS

• To the touch an exothermic reaction would feel
  HOT because heat is being released to the
  surroundings
• In a chemical reaction that is exothermic, the
  energy would be represented in the chemical
  equation on the product side of the reaction
  (heat is formed/released).
• C3H8(g) 5O2(g) ? 3CO2(g) 4H2O(g) 2043 kJ

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ENDOTHERMIC REACTIONS

• To the touch an endothermic reaction would feel
  cold because heat is being absorbed from the
  surroundings.
• In a chemical reaction that is endothermic, the
  energy would be represented in the chemical
  equation on the reactants side of the reaction
  (since heat is being absorbed/taken in).
• C(s)H2O(g) 113 kJ ? CO(g)H2(g)

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Identify each of the following reactions as
either an endothermic reaction or an exothermic
reaction.

• ) C2H4 ? 2C 2H2 52.3 kJ
• b) B2H6 6H2O ? 2H3BO3 6H2 493.4 kJ
• c) 2Fe 3CO2 26.8 kJ ? Fe2O3 3CO
• d) Br2 Cl2 29.4 kJ ? 2BrCl

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5 MAIN CLASSIFICATIONS OF CHEMICAL REACTIONS

• Synthesis Reactions
• Decomposition Reactions
• Combustion Reactions
• Single-Replacement Reactions
• Double-Replacement Reactions

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Synthesis Reactions

• Always Have 1 Product
• General Format A B ? AB
• Predicting the Product
• The reactants come together to form one product
• If the reactants are a metal a nonmetal then
  they will form an ionic compoundget the charges
  crisscross
• If they are not, the product will be given

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Examples of Synthesis Reactions

• Na Cl2?

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Examples of Synthesis Reactions

• H2 O2 ?
• Al S ?

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Decomposition Reactions

• Always Have 1 Reactant
• General Format AB ? A B
• Predicting the Product Separate the reactant
  into its elements
• Example of Decomposition
• C6H12O6 ? C H2O

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Examples of Decomposition

• MgS ?
• Li2O ?

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Combustion Reactions

• Always have Oxygen (O2) as a reactant
• General Formats
• CxHy O2 ? CO2 H2O
• A O2 ? AxOy
• Predicting the product
• If its combustion between a hydrocarbon oxygen
  the reaction will produce CO2 H2O
• If its combustion between an element and oxygen
  it is a synthesis reactionget your charges and
  crisscross

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COMBUSTION REACTIONS

• Always has elemental oxygen (O2) as one of the
  reactants
• Example
• Burning of methane
• CH4 O2? CO2 H2O
• Burning of propane
• C3H8 O2 ? CO2 H2O
• Synthesis of sodium oxide
• Na O2 ? Na2O

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Examples

• C2H2 O2 ?
• Na O2 ?

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Single Replacement Reactions

• Always have 1 element and 1 compound as the
  reactants and as the products
• General Format A BC ? B AC
• Activity Series Lists the elements in order of
  their reactivity. The more reactive elements can
  replace the less reactive elements
• Elements higher on the list can replace elements
  lower on the list

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Which element can replace the other in a chemical
reaction?

• Tin or Barium
• Iodine or Bromine

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Single Replacement Reactions

• General Format A BC ? B AC
• Predicting the Product If the single element is
  more reactive than the similar element in the
  compound, those two elements will switch spots.
  This will form an element and a new ionic
  compound.

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Examples of Single Replacement Reactions

• Zn Cu(NO3)2 ?
• Cu Zn(NO3)2 ?
• Cu AgNO3 ?

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More examples of Single Replacement Reactions

• Zn(s) H2SO4(aq) ?
• Na(s) H2O(l) ?
• Sn(s) NaNO3(aq) ?
• Cl2(g) NaBr(aq) ?

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Double Replacement Reactions
?

• Always have 2 compounds in the reactants
  (typically ionic compounds) and 2 compounds in
  the products
• General Format AX BY ? BX AY
• Double replacement reactions occur if one of the
  products will be a molecular compound (such as
  H2O), a precipitate or a gas.
• Predicting the product The metals will switch
  placesget the charges and crisscross
• Types of products water, gas, or precipitate

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Double Replacement Reactions
?

• Precipitate An insoluble solid formed from two
  aqueous solutions.

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SOLUBILITY RULES

• Solubility Rules On the solubility chart on
  back of your
• periodic table
• s precipitate, aq aqueous (not a
  precipitate)

GENERAL SOLUBILITY RULES
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Examples of Double Replacement Reactions

• BaCl2(aq) K2CO3(aq) ?
• FeS(s) HCl(aq) ?
• CaCO3 HCl ?

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DISSOCIATION

• Double replacement reactions occur between 2
  ionic compounds in aqueous solution.
• When ionic compounds dissolve in water, they
  dissociate into the cation and anion of the
  compound.
• DISSOCATION The separation of ions that occurs
  when an ionic compound dissolves

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Complete Ionic Equation

• An equation that shows dissolved ionic compounds
  as dissociated free ions.
• Chemical Equation
• AgNO3(aq) NaCl(aq) ? AgCl(s) NaNO3(aq)
• Complete Ionic Equation
• Ag(aq) NO3-(aq) Na(aq) Cl-(aq) ? AgCl(s)
  Na(aq) NO3-(aq)

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Net Ionic Equation

• An equation for a reaction in solution that shows
  
• only those particles that are directly involved
  in the
• chemical change.
• A net ionic equation shows only the particles
  involved in the
• reaction and is balanced with respect to both
  mass and
• charge.
• Spectator Ion An ion that appears on both sides
  of an equation and is not directly involved in
  the reaction.

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• Chemical Equation
• AgNO3(aq) NaCl(aq) ? AgCl(s) NaNO3(aq)
• Complete Ionic Equation
• Ag(aq) NO3-(aq) Na(aq) Cl-(aq) ? AgCl(s)
  Na(aq) NO3-(aq)
• Any ions that appear on both sides, cross out,
  they are spectator
• ions and are not involved in the chemical
  reaction.

Net Ionic Equation The ionic equation rewritten
without the spectator ions. Ag(aq) Cl-(aq) ?
AgCl(s)
Once the net ionic equation is written, make sure
all atoms are balanced and all charges are
balanced.
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• Example 1
• Chemical Equation
• Pb(s) AgNO3(aq) ? Ag(s) Pb(NO3)2(aq)
• Complete Ionic Equation
• Net Ionic Equation

Once the net ionic equation is written, make sure
all atoms are balanced and all charges are
balanced.
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• Example 2
• Chemical Equation
• FeCl3(aq) KOH(aq) ? Fe(OH)3(s) KCl(aq)
• Complete Ionic Equation
• Net Ionic Equation

Once the net ionic equation is written, make sure
all atoms are balanced and all charges are
balanced.
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• Example 3
• Word Equation
• sodium carbonate barium nitrate ?
• Chemical Equation
• Complete Ionic Equation
• Net Ionic Equation

Once the net ionic equation is written, make sure
all atoms are balanced and all charges are
balanced.
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Exceptions to the Rules

• Many synthesis reactions are also combustion
  reactions but not all combustion reactions are
  synthesis reactions
• There are other reactions that do not fit neatly
  into 1 of the 5 categories.

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5 GENERAL FORMATS

• Synthesis A B ? AB
• 1 product
• Decomposition AB ? A B
• 1 reactant
• Combustion CxHy O2 ? CO2 H2O
• X O2 ? XyO
• O2 is one of the reactants
• Single Replacement A BC ? B AC
• 1 element 1 compound on both sides of the rxn
• Double Replacement AB CD ? CB AD
• 2 compounds on both sides of the rxn