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Chapter 11.1: Describing
Chemical Reactions
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Quickwrite
Write
down everything you
already know about chemical
reactions.
1:30
minutes
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Writing Chemical Equations
A
chemical equation occurs when
one more more reactants change
into one more more new
substances called products.
An
arrow in a reaction means
yields gives, or reacts to produce.
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EXAMPLE
Write
a word equation that
describes the following reactions:
Acetylene
reacts with oxygen to
produce carbon dioxide and water.
C2H2 + O2  CO2 + H2O
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EXAMPLE
When
heated, Mercury (III) Oxide
reacts to form mercury and water.
Hg2O  Hg + O2
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What is a chemical equation?
A
chemical equation is a
representation of a chemical reaction;
the formulas of the reactants (on the
left) are connected by an arrow with
the formulas of the products (on the
right).
Reactants
 Products
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Define Skeleton Equation.
A
chemical equation that does not
indicate the relative amounts of the
reactants and products.
Identify
the reactant(s) & product(s) in
the chemical equation:
Li
+ Br  LiBr
 Reactant(s)
= Li and Br
 Product = LiBr
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A catalyst
A
catalyst is a substance that can
be added to speed up the
reaction but is not used up in a
reaction. It is neither a product or
a reactant.
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Table 11.1
Symbol
Explanation
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Used to separate 2 reactants or 2 products

“yields”, separates reactants from products
<-->
Used in place of “” for reversible reactions
(s)
Reactant or product in solid phase
(l)
Reactant or product in liquid phase
(g)
Reactant or product in gaseous phase
(aq)
Aqueous solution (dissolved in water)
Indicates that heat is supplied to the reaction
A formula written above or below a yield sign
indicates its use as a catalyst (in tis example, Sulfuric
Acid).
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PLEASE ADD TO THE BOTTOM OF THIS
PAGE
 “Diatomic
Molecule” – Molecules made up
of 2 atoms.
 EXAMPLES YOU
NEED TO KNOW:
 Oxygen (gas) – O2
 Nitrogen (gas) – N2
 Hydrogen (gas) – H2
 Fluorine (gas) – F2
 Chlorine (gas) – Cl2
 Iodine (gas) – I2
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On Your Own
3 minutes for this
Using
the symbols in Table 11.1 on
Page 2, write a skeleton equation for
the following reactions.
 Hydrochloric
acid reacts with zinc to
produce aqueous zinc (II) chloride and
hydrogen gas.
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On Your Own
Using
the symbols in Table 11.1 on
Page 2, write a skeleton equation for
the following reactions.
 Sulfur
burns in oxygen to form sulfur
dioxide
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Balancing Chemical Equations
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Balancing Chemical Equations
EACH
SIDE HAS THE
SAME NUMBER OF
PARTS.
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To write a balanced equation:
First: write
Then: use
the skeleton equation.
coefficients to balance
the equation so that so that it
obeys the conservation of mass
(mass cannot be created or
destroyed).
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Balancing Chemical Equations
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Balancing Chemical Equations
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