CHEMICAL EQUATIONS

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CHEMICAL EQUATIONS
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Water and what is known from its equation.
2H2 O2 ? 2H2O
hydrogen oxygen ? water
4 atoms H 2 atoms O ? 4 atoms H 2 atoms O
2 molecules H 1 molecule O ? 2 molecules water
2 moles H 1 mole O ? 2 moles water
4 amu H 32 amu O ? 36 amu water
4 grams H 32 grams O ? 36 grams water

Note that molecules and moles always have the
SAME RATIOS
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CHEMICAL REACTIONS

• one or more substances are changed into different
  substances
• Represented by chemical equations
• 2H2 (g) O2(g) ? 2H2O(g)
• ?REACTANTS PRODUCTS ?

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CHEMICAL EQUATIONS

• Show the substances undergoing change and the
  result(s).
• Show relative amts. of elements/cmpds. that take
  part in the changes coefficients
• See Symbols Used in Chem. Rxn. handout

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Writing Chemical Equations
11.1
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Writing Chemical Equations
11.1

• iron oxygen ? iron(III) oxide

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Writing Chemical Equations
11.1

• Hydrogen Peroxide ? Water and Oxygen

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The PVC Method to WRITING A BALANCED CHEMICAL
EQUATION

• Pair the elements properly
• Valences give subscripts
• Coefficients balance the equation

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WRITING A BALANCED CHEMICAL EQUATION

• Tips
• Start with element that appears only once on each
  side.
• Save oxygen and hydrogen for last

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Lithium aluminum hydride reacts with water to
produce lithium hydroxide, aluminum hydroxide and
hydrogen gas.

• LiAlH4 H2O ? LiOH Al(OH)3 H2
• LiAlH4 4H2O ? LiOH Al(OH)3
• 
  H2
• LiAlH4 4H2O ? LiOH Al(OH)3
• 
  4H2
• Note that hydrogen is diatomic when not bonded
  to other elements.

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Diatomic Molecules

• Harvey BrOFINCl

H. BrOFINCl
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Persistent difficulty ?

• Check all FORMULAS to make sure they are correct
• K2(SO4) v K2(SO3)

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Ammonia reacts with oxygen gas to produce
nitrogen dioxide and water.

• NH3 O2 ? NO2 H2O
• 2NH3 O2 ? NO2 3H2O
• 2NH3 O2 ? 2NO2 3H2O
• 2NH3 7/2O2 ? 2NO2 3H2O
• 4NH3 7O2 ? 4NO2 6H2O

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Synthesis
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Common Types of Chemical Reactions

• Synthesis
• two or more simple compounds combine to form a
  more complicated one
• General form A B ---gt AB
• Iron and sulfur to form iron (II) sulfide
• 8 Fe S8 ---gt 8 FeS

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Decomposition
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Common Types of Chemical Reactions

• Decomposition
• opposite of a synthesis reaction
• complex molecule breaks down to make simpler ones
  
• General form AB ---gt A B
• Hydrogen peroxide decomposes to water and oxygen
  gas
• H2O2 ? H2O O2

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Single Replacement
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Common Types of Chemical Reactions

• Single Replacement
• one element trades places with another element in
  a compound
• General form A BC ---gt AC B, or
  A- BC ---gt BA C
• Zinc replaces copper in copper sulfide solution
• Zn CuSO4 ? ZnSO4 Cu

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Double Replacement
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Common Types of Chemical Reactions

• Double Replacement
• cations (positive ions) of two different
  molecules switch places, forming two entirely
  different compounds
• General form
• AB CD ---gt AD CB
• Sodium Chloride (salt) solution reacts with
  silver nitrate to produce silver chloride and
  sodium nitrate.
• NaCl AgNO3 ? AgCl NaNO3

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Common Types of Chemical Reactions

• Combustion
• oxygen combines with a compound containing
  carbon, hydrogen and sometimes oxygen
• forms water and carbon dioxide.
• General Form CxHy ? CO2 H2O
• Exothermic
• Burning of naphthalene
• C10H8 12 O2 ---gt 10 CO2 4 H2O

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Review and Foreshadow

• Video
• Logic and rules for balancing chemical equations
  are reviewed
• Types of chemical reactions are introduced
• Take Notes
• Quiz (10 points) _at_ end of video
• Name
• Period
• Number 1-10

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Decomposition Special Cases

• Anions and cations do not separate as expected.
• X any metal

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Metal carbonates

• XCO3 ? XO CO2
• metal oxide carbon dioxide
• CaCO3 ? CaO CO2

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Metal hydroxides

• XOH ? XO H2O
• metal oxide water
• Ca(OH)2 ? CaO H2O

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Metal chlorates

• XClO3 ? XCl O2
• metal chloride oxygen gas
• Ca(ClO3)2 ? CaCl2 3O2

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Single Replacement Reactions

• A BC ---gt AC B, or
• A- BC ---gt BA C
• Are the free elements always able to replace the
  element in the compound?
• How can we tell when / if the free elements will
  successfully replace the element in the compound?

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Activity Series partial listing
Metals Decreasing Activity Halogens
lithium ? fluorine
potassium ? chlorine
calcium ? bromine
sodium ? oxygen
magnesium ? iodine
aluminum ? sulfur
zinc ?
chromium ?
iron ?
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Will these reactions occur?

• ZnCO3 H2 ??
• ZnCO3 H2 ?N.R.
• AgCl Mg ??
• 2AgCl Mg ?MgCl2 2Ag

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Replacing HYDROGEN in WATER

• Water is unusually stable.
• Replacing the hydrogen in water depends on
• Placement of free element on activity series, and
• TEMPERATURE

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Replacing HYDROGEN in WATER

• lt 175 oC
• X H2O ? XOH H2
• Metal hydroxide hydrogen gas
• Ca 2H2O ? Ca(OH)2 H2
• gt 175oC
• X H2O ? XO H2
• Metal oxide hydrogen gas
• Ca H2O ? CaO H2

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Double Replacement Reactions

• AB CD ---gt AD CB
• When a double replacement reaction occurs one of
  the following are produced
• gas
• precipitate
• an insoluble solid that forms when two liquids
  are mixed
• water
• These rxn also called acid-base rxn

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SOLUBILITY

• The property of a substance to dissolve
• Water
• Universal solvent
• Solubility Table - handout
• NaCl AgNO3 ? NaNO3 AgCl
• 2NaCl Fe(NO3)2 ? 2NaNO3 FeCl2
• ? NR (no double
  replacement
• 
  products made)

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Predicting Reaction Products

• Analyze the reactants.
• Decide what pattern of chemical reaction the
  reactants will fit.
• Na and H2SO4
• a single element and a compound fit the
• single replacement pattern.
• H2 and O2
• two elements fit the synthesis pattern.

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• Use the pattern to decide which elements will go
  together.
• REMEMBER to refer to the Activity Series for
  single replacement reactions.
• Na H2SO4 ?
• Na replaces H Na stronger than H H becomes
  lone element.
• 2Na H2SO4 ? Na2SO4 H2

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• Use valences to form good chemical formulas to
  represent the products.
• The sum of the valences equals zero in a chemical
  formula.
• Na1 SO4-2
• 2Na H2SO4 ? Na2SO4 H2
• Write the diatomic elements as H2, Br2, O2, F2,
  I2, N2, and Cl2. when they are by themselves..
  (Henry BrOFINCl)
• 2H2 O2 ? 2H2O

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• Balance the equations using coefficients
• (BIG numbers placed in FRONT of the chemical
  formula.)
• 2Na H2SO4 ? Na2SO4 H2
• 2H2 O2 ? 2H2O
• Balance H, O last.

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Nuclear Equations

• Nuclear equations result in the change of one
  element into another
• transmutation
• 238 number of protons neutrons
• 92 U number of protons (determines identity
  of atom)

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a particle decay

• 238 234 4
• 92 U ? 90 Th 2He
• thorium a particle

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ß particle decay

• 234 234
  0
• 90 Th ? 91 Pa -1e-
• protactinium ß particle
• Decay continues until a stable substance is
  reached.

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K capture decay

• 100 0
  100
• 46 Pd -1e- ? 45 Rh

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Rules for balancing nuclear equations

• The sum of the mass numbers (top) is the same on
  both sides of the equation.
• The sum of the electric charges (bottom) is the
  same on both sides of the equation.

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Find the unknown product

• 18 0
• 9F ? 1 e- ?
• Find the mass
• 18 0 x
• 18 x
• 18 0 18
• 9 F ? 1e- ?

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230?V X

• Find the charge
• 9 1 x
• 8 x
• 18 0 18
• 9F ? 1e- 8 ?

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• Find the element
• 18 0 18
• 9F ? 1e- 8 O