1. Copy down HW 2. Take out HW

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1. Copy down HW2. Take out HW COMPARE
your work to your table partners

• BELLWORK

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• Chemical Reactions Equations

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Chemical Equations

• Shows what takes place during a
• chemical reaction
• Reactant (substances reacting) on left
• Arrow - (?) at center yields or produces
• Products (new substances formed) on
• right

• A B ? C D

PRODUCTS
REACTANTS
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Coefficients how many? appears in FRONT of
the formula

• molecules for covalent substances
• moles of atoms
• units for ionic substances

3CO2 ? 2Mg ? 4MgO ?
3 molecules of carbon dioxide 2 moles of
magnesium 4 units of magnesium oxide

• Phases
• solid (s), liquid (l), gas (g), Aqueous (aq)

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Writing Equations
CH4 2O2 ? CO2 2H2O

• Names of reactants methane oxygen
• Names of products carbon dioxide water

• How many of each (coefficient)
• __CH4 ____O2 ____CO2 ___H2O

• Ratio of coefficients ___ ____ ___ ___

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Expressing Chemical Equations

• Word carbon oxygen yields carbon
• dioxide
• Remember your diatomic gases
• (BrINClHOF)

Formula C O2 ? CO2
Diagram

?
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Expressing Equations with words
Zn(s) 2HCl(aq) ? ZnCl2(aq) H2(g)

• How many?
• Of what?
• In what state?

One atom of solid zinc
reacts with
two molecules of aqueous hydrochloric acid

• to produce

one unit
of aqueous zinc chloride
and one
molecule of hydrogen gas.
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Exothermic Endothermic Processes see RB pg
34 table 2.5

• Exothermic release energy surrounding temp
  increases
• A B ? AB energy
• CH4 3 O2 ? CO2 2 H2O energy
• Endothermic require/absorb energy surrounding
  temp decreases
• AB energy? A B
• H2O(s) energy ? H2O (l)

Endothermic video http//www.youtube.com/watch?v5
RJLvQXce4A
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Law of Conservation of Mass/Matter/Energy

• Matter is neither created nor destroyed in
  chemical reactions. In any chemical total numbers
  kinds of atoms must remain unchanged in the
  reaction. This is called a balanced equation.
• Charge, energy, mass, and atoms are conserved
  (unchanged) in balanced reactions

4 H 2 O
4 H 2 O
36 g
4 g
32 g
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Signs of a Chemical Reaction

• Evolution of heat and light
• Formation of a gas
• Formation of a precipitate
• Color change

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Chemical Change chemical composition changes
Physical Change chemical composition remains
the same

• Examples of a physical change
• Ripping, tearing, breaking
• Boiling, melting, freezing, vaporing a substance
  (a phase change)
• dissolving

• Signs of a Chemical Reaction
• Evolution of heat and light
• Formation of a gas
• Formation of a precipitate
• Color change

• Examples of a chemical change
• Burning, rusting, oxidizing
• Flammable, explosive, reacting

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II. Balancing Equations

• Chemical Reactions

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A. Balancing Steps

• 1. Write the unbalanced equation.
• 2. Count atoms on each side.
• 3. Add coefficients to make s equal.
• Coefficient ? subscript of atoms
• 4. Reduce coefficients to lowest possible
  ratio, if necessary.
• 5. Double check atom balance!!!

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B. Helpful Tips

• Balance one element at a time.
• Update ALL atom counts after adding a
  coefficient.
• If an element appears more than once per side,
  balance it last.
• Balance polyatomic ions as single units.
• 1 SO4 instead of 1 S and 4 O

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C. Balancing Example

• Aluminum and copper(II) chloride react to form
  copper and aluminum chloride.

3
3
2
2
1 1 1 1 2
3
2 ?
? 2 ? 6
3 ? 6 ?
? 3
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III. Types of Chemical Reactions

• Chemical Reactions

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A. Combustion

• the burning of any substance in O2 to produce heat

A O2 ? B
CH4(g) 2O2(g) ? CO2(g) 2H2O(g)
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A. Combustion

• Products
• contain oxygen
• hydrocarbons form CO2 H2O

Na(s) O2(g) ?
Na2O(s)
4 2
C3H8(g) O2(g) ?
CO2(g) H2O(g)
5 3
4
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B. Synthesis

• the combination of 2 or more substances to form a
  compound
• only one product

A B ? AB
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B. Synthesis

• H2(g) Cl2(g) ? 2 HCl(g)

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B. Synthesis

• Products
• ionic - cancel charges

Al(s) Cl2(g) ?
AlCl3(s)
2 3 2
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C. Decomposition

• a compound breaks down into 2 or more simpler
  substances
• only one reactant

AB ? A B
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C. Decomposition

• 2 H2O(l) ? 2 H2(g) O2(g)

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C. Decomposition

• Products
• binary - break into elements

KBr(l) ?
K(s) Br2(l)
2 2
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D. Single Replacement

• one element replaces another in a compound
• metal replaces metal ()
• nonmetal replaces nonmetal (-)

A BC ? B AC
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D. Single Replacement

• Cu(s) 2AgNO3(aq) ? Cu(NO3)2(aq) 2Ag(s)

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D. Single Replacement

• Products
• metal ? metal ()
• nonmetal ? nonmetal (-)
• free element must be more active (check activity
  series-Table J)

Fe(s) CuSO4(aq) ?
Cu(s) FeSO4(aq)
Br2(l) NaCl(aq) ?
N.R.
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E. Double Replacement

• ions in two compounds change partners
• cation of one compound combines with anion of the
  other

AB CD ? AD CB
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E. Double Replacement

• Pb(NO3)2(aq) K2CrO4(aq) ? PbCrO4(s) 2KNO3(aq)

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E. Double Replacement

• Products
• switch negative ions
• one product must be insoluble (check solubility
  table)

Pb(NO3)2(aq) KI(aq) ?
PbI2(s) KNO3(aq)
2
2
NaNO3(aq) KI(aq) ?
N.R.