Chemical

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Chapter 9 Chemical Reactions
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Chemical reaction
process by which the atoms of one or more
substances are rearranged to form different
substances
same as chemical change
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Chemical reaction
starting substances are reactants
substances formed or produced during reaction are
products
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Evidence of a chemical reaction (change)
1. temperature change
2. color change

• production of a gas
• (odor/bubbles)

4. formation of a solid (precipitate)
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Chemical equation
A statement using chemical formulas to describe
the identities and relative amounts of the
reactants and products involved in the chemical
reaction.
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Silver metal reacts with hydrogen sulfide gas in
the air to form solid silver sulfide and hydrogen
gas.
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Some pure elements exist as diatomic molecules.
H2, N2, O2, F2, Cl2, Br2, I2
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-gens hydrogen oxygen nitrogen
halogens (group 17)
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Write formulas / symbols for the following
magnesium
nitrogen
carbon dioxide
fluorine
sodium chloride
sulfur
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Law of Conservation of Mass
Mass is neither created nor destroyed during a
chemical reaction it is conserved.
Total mass of reactants always equals total mass
of products.
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Therefore, chemical equations must be balanced
same number of atoms of each element on each side
of arrow.
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To balance a chemical equation

• Count number of
• atoms of each
• element on each
• side of arrow.

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• Add coefficients in
• front of formulas.
• Must be lowest whole
• number ratio.

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Iron metal reacts with oxygen gas to form
iron(III) oxide (rust.)
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Classifying chemical reactions
useful for understanding chemical reactions and
for predicting products
five general types of reactions
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Synthesis reactions
two or more substances react to form a single
product
A B ? AB
Key one product
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Synthesis reaction
Zinc metal reacts with solid iodine to form solid
zinc iodide.
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Decomposition reactions
a single compound breaks down into two or more
simpler substances (elements or compounds)
AB ? A B
Key one reactant
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Decomposition reactions
often must add energy (heat/electricity) to make
reaction occur
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Decomposition reaction
When heated, solid potassium chlorate reacts to
form solid potassium chloride and oxygen gas.
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Single-replacement reactions
one element replaces another element in a compound
A BX ? AX B
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Single-replacement reactions
more active element replaces less active element
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When balancing replacement reactions keep
polyatomic ions intact and write water as HOH
(hydrogen and a hydroxide.)
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Single-replacement reaction
Copper metal reacts with aqueous silver nitrate
to produce silver metal and aqueous copper(II)
nitrate.
copper replaces silver
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Single-replacement reaction
Sodium metal reacts with water to form sodium
hydroxide and hydrogen gas.
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Double-replacement reactions
Exchange of ions between aqueous solutions of two
compounds.
AX BY ? AY BX
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Double-replacement reactions
Aqueous solutions of lead(II) nitrate and
potassium iodide react to form aqueous potassium
nitrate and a precipitate of lead(II) iodide.
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Combustion reactions
substance reacts rapidly with oxygen gas and
releases energy in form of heat and light
may also be synthesis reaction
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Iron metal reacts with oxygen gas to form
iron(III) oxide (rust.)
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Iron metal burns in oxygen gas to form iron(III)
oxide.
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Combustion reactions
If reactant contains carbon, then products of a
combustion reaction are always carbon dioxide gas
and water vapor.
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Sucrose (C12H22O11) burns in oxygen.
Products are carbon dioxide gas and water vapor.
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Single-replacement reactions
more active element replaces less active element
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A more active metal will replace a less active
metal.
Will the following single-replacement reaction
occur?
Fe(s) Cu(NO3)2(aq) ?
Yes, iron is more active than copper.
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Fe(s) Cu(NO3)2(aq) ? Cu(s)
Fe(NO3)2(aq)
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A more active nonmetal will replace a less active
nonmetal.
Will the following single-replacement reaction
occur?
Cl2(g) NaBr(aq) ?
Yes, chlorine is more active than bromine.
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Cl2(g) 2NaBr(aq) ? Br2(g)
2NaCl(aq)
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Will the following single-replacement reaction
occur?
Al(s) MgCl2(aq) ?
No, aluminum is not more active than magnesium.
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Solid calcium metal reacts with water to
produce aqueous calcium hydroxide and hydrogen
gas.
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When aqueous solutions of sulfuric acid and
barium chloride are mixed, a precipitate of
barium sulfate and aqueous hydrochloric acid are
formed.