Chemical Equations

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Chemical Equations Reactions
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Lecture Outline Chemical Equations Reactions
Lecture Outline Chemical Equations Reactions
student notes outline
textbook questions
Lecture Outline Chemical Equations Reactions
textbook questions
Keys
text
http//www.unit5.org/chemistry/Equations.html
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Chemical Reactions

• You should be able to
• Classify reactions by type.
• Write a balanced molecular equation, complete
  ionic equation,
• and a net ionic equation.
• Balance oxidation-reduction reactions.
• Predict if a precipitate will form using the
  solubility rules.
• Predict products of reactions given the chemical
  names of the
• reactants.

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Organize Your Thoughts
Chemical reactions
Chemical equations
Chemical equations

• Synthesis
• Decomposition
• Single replacement
• Double replacement
• Combustion

• Balancing equations
• Predicting products
• from reactants

Packard, Jacobs, Marshall, Chemistry Pearson AGS
Globe, page 175
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Describing a Chemical Reaction

• Indications of a Chemical Reaction
• Evolution of heat, light, and/or sound
• Production of a gas
• Formation of a precipitate
• Color change

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Signs of Chemical Reactions
There are five main signs that indicate a
chemical reaction has taken place

release
input
change in color
change in odor
production of new gases or vapor
input or release of energy
difficult to reverse
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Chemical Equations
aluminum oxide
product
Depict the kind of reactants and products and
their relative amounts in a reaction.
reactants
The letters (s), (g), and (l) are the physical
states of compounds.
The numbers in the front are called
stoichiometric coefficients.
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Chemical Equations
aluminum oxide sandpaper
4 g Al 3 g O2 yield 2 g Al2O3
This equation means
4 Al atoms 3 O2 molecules yield 2
molecules of Al2O3
or
4 Al moles 3 O2 moles yield 2 moles of
Al2O3
2 mol Al2O3_at_102g/mol
4 mol Al_at_27g/mol
3 mol O2_at_32g/mol
108 g 96 g
204 g
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Chemical Equations
Because the same atoms are present in a reaction
at the beginning (reactants) and at the end
(products), the amount of matter in a system
does not change.
The Law of Conservation of Matter
Kotz web
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Chemical Equations
Because of the principle of the conservation of
matter,
An equation must be balanced.
It must have the same number of atoms of the
same kind on both sides.
Lavoisier, 1788
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Characteristics of Chemical Equations

• The equation must represent known facts.
• The equation must contain the correct formulas
  for the reactants and products.
• The law of conservation of mass must be satisfied.

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Chemical Equations

• Reactants the substances that exist before a
  chemical change (or reaction) takes place.
• Products the new substance(s) that are formed
  during the chemical changes.
• CHEMICAL EQUATION indicates the reactants and
  products of a reaction.

REACTANTS ? PRODUCTS
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Word Equations

• A WORD EQUATION describes chemical change using
  the names of the reactants and products.

Write the word equation for the reaction of
methane gas with oxygen gas to form carbon
dioxide and water.
carbon dioxide water
methane oxygen
Reactant
Product
O2
2
CO2
H2O
2
CH4


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Unbalanced and Balanced Equations
H
Cl
Cl
Cl
H
H
H2 Cl2 ? 2 HCl
(balanced)
(unbalanced)
H2 Cl2 ? HCl
2
1
2
2
2
1
2
2
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Visualizing a Chemical Reaction
2
Na Cl2
NaCl
2
?
10
5
10
10
5
10
___ mole Cl2
___ mole NaCl
___ mole Na
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Visualizing a Chemical Reaction
2
Na Cl2
NaCl
2
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Meaning of Chemical Formula
Chemical Symbol Meaning
Composition
H2O One molecule of water
Two H atoms and one O atom
2 H2O Two molecules of water
Four H atoms and two O atoms
H2O2 One molecule of hydrogen peroxide
Two H atoms and two O atoms
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Balancing Chemical Equations

• Balanced Equation one in which the number of
  atoms of each element as a reactant is equal to
  the number of atoms of that element as a product

What is the relationship between conservation of
mass and the fact that a balanced equation will
always have the same number of atoms of each
element on both sides of an equation?
Determine whether the following equation is
balanced.
2 Na H2O ? 2 NaOH H2
2 Na 2 H2O ? 2 NaOH H2
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Balancing Chemical Equations

• Write a word equation for the reaction.
• Write the correct formulas for all reactants and
  products.
• Determine the coefficients that make the equation
  balance.

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Guidelines for Balancing Chemical Equations
1) polyatomic ions first
?
2) even / odd
(make all even)
3) H2O Mg(OH)2
2
H-OH vs.
4) single elements last
Example need 13 oxygen atoms
Multiply by O2 13
2
21
?
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(NH4)3PO4 Mg(OH)2 ? Mg3(PO4)2
NH4OH

2
3
ammonium phosphate
magnesium hydroxide
magnesium phosphate
ammonium hydroxide
NH41
OH1-
Now you try
AlCl3 Li2CO3 ? Al2(CO3)3
LiCl
3
2
6
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Balancing Chemical Equations
          Balancing Chemical Equations
          Balancing Equations (visual)
          Balancing Chemical Equations
          www.funbasedlearning.com
Keys (visual)
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Write a balanced equation for the reaction
between chlorine and sodium bromide to produce
bromine and sodium chloride.

• 1) Write a word equation for the reaction.

chlorine sodium bromide ? bromine
sodium chloride
2) Write the correct formulas for all reactants
and products.
Cl2 NaBr ?
Br2 NaCl
3) Determine the coefficients that make the
equation balance.
Cl2 2 NaBr ?
Br2 2 NaCl
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Write the balanced equation for the reaction
between aluminum sulfate and calcium chloride to
form a white precipitate of calcium sulfate.
1) Write a word equation for the reaction.
?
?
aluminum sulfate calcium chloride ? calcium
sulfate
aluminum chloride
2) Write the correct formulas for all reactants
and products.
Al2(SO4)3 CaCl2 ?
CaSO4 AlCl3
3) Determine the coefficients that make the
equation balance.
Al2(SO4)3 3 CaCl2 ? 3 CaSO4
2 AlCl3
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CH4 2 O2 ? CO2 2 H2O
Reactants Products 1 C atom
1 C atom 4 H atoms 4 H
atoms 4 O atoms 4 O atoms
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Reactants ? Products
catalyst speeds up reaction
2
2
Unbalanced
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Showing Phases in Chemical Equations
H2O(s) H2O(l) H2O(g)

• Solid Phase the substance is relatively rigid
  and has a definite volume and shape. NaCl(s)
• Liquid Phase the substance has a definite
  volume, but is able to change shape by flowing.
  H2O(l)
• Gaseous Phase the substance has no definite
  volume or shape, and it shows little response to
  gravity. Cl2(g)

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Additional Symbols Used in Chemical Equations

• Yields indicates result of reaction
• Used to indicate a reversible reaction
• A reactant or product in the solid state
• also used to indicate a precipitate
• Alternative to (s), but used only to indicate a
  precipitate
• A reactant or product in the liquid state
• A reactant or product in an aqueous solution
• (dissolved in water)
• A reactant or product in the gaseous state

(s)
(l)
(aq)
(g)
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Additional Symbols Used in Chemical Equations
Alternative to (g), but used only to indicate a
gaseous product Reactants are
heated Pressure at which reaction is carried
out, in this case 2 atm Pressure at which
reaction is carried out exceeds
normal atmospheric pressure Temperature at
which reaction is carried out, in this case 0
oC Formula of catalyst, in this case manganese
(IV) oxide, used to alter the rate of the
reaction
D
2 atm
pressure
0 oC
MnO2
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Solubility Ionic Equations Cover the answers,
work the problem, then check the answer. 1.
Dissolve ammonium nitrate 2. Precipitate
cupric hydroxide 3. Dissolve chromium
thiocyanate 4. Precipitate lead arsenate 5.
Dissolve silicon permanganate 6. Precipitate
zinc phosphate
NH4NO3 (s) ---gt NH41 (aq) NO3-1 (aq)
Cu2 (aq) 2OH-1 (aq) ---gt Cu(OH)2 (s)
Cr(SCN)3 (s) ---gt Cr3 (aq) 3SCN-1 (aq)
3Pb2 (aq) 2AsO4-3 (aq) ---gt Pb3(AsO4)2 (s)
Si(MnO4)4 (s) ---gt Si4 (aq) 4MnO4-1 (aq)
3Zn2 (aq) 2PO4-3 (aq) ---gt Zn3(PO4)2 (s)