Download Chemical Reactions

Chemical Reactions:
Chp 8
1
Describing Chemical Change:
• To understand chemical
reactions we need to describe
them in writing.
2
Describing a Chemical Change:
• Chemical reaction = one or
more substances change into
one or more new substances
3
Describing Chemical Change:
• Reactants vs. Products
• Reactants = those substances
that are reacting or changing
• Products = those substances that
are being formed from the
reactants
4
Describing Chemical Change:
• In writing a chemical reaction,
an arrow is used to separate the
reactants from the products
• The arrow (
) = yields, gives
or reacts to produce
5
Describing Chemical Change
• Remember: All chemical
reactions must follow the law of
conservation of matter
• What is this law?
6
Describing Chemical Change:
• Chemical equations: using
chemical formulas to describe
in writing a chemical reaction
• The arrow separates the
formulas of the reactants from
the formulas of the products
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Describing Chemical Change:
• Skeleton equation:
–Does not indicate relative
amounts
–Shows just the formulas of the
reactants and products
• Example:
Fe + O2
Fe2O3
8
Describing Chemical Change:
• You can indicate the state of each
substance by using symbols to
represent solid (s), liquid (l), gas (g)
and aqueous (aq)
• Example:
Fe(s) + O2(g)
Fe2O3(s)
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Describing Chemical Change:
• Catalyst ?
• A substance that speeds up the
rate of a reaction but is not used
up in the reaction
10
Balancing Chemical Equations:
• If there is no indication of the
quantity of reactants and
products in a equation, it is
unbalanced
11
Balancing Chemical Equations:
• Balanced equations usually
contain coefficients:
• Coefficients = numbers placed
in front of the symbols for the
respective parts
12
Balancing Chemical Equations:
• Balanced chemical equation =
has the same number of atoms
of each elements on each side
of the equation
• 4 Fe(s) + 3 O2(g)  2 Fe2O3(s)
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Balancing Chemical Equations:
• Example:
–C(s) +
O2(g)
CO2(g)
• Each side of the equation has
the same number of carbon and
oxygen atoms
• The equation is balanced
14
Balancing Chemical Equations:
• Rules: page 208
15
Balancing Chemical Equations:
• Additional rules:
• 1. Solve the more complicated
compounds first
• 2. Any polyatomic ions present
on each side of the equation
count as one unit
• 3. Solve the single elements last
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