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Chemical Reactions
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Observing Chemical
Reactions
Evidence:
1) The colour changes
2) Bubbles
A gas is produced
3) The mixture gets hotter (EXOTHERMIC)
or colder (ENDOTHERMIC)
4) A solid (PRECIPITATE) forms from two
aqueous solutions
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Observing Chemical
Reactions
Evidence:
1) The colour changes
2) Bubbles
A gas is produced
3) The mixture gets hotter (EXOTHERMIC)
or colder (ENDOTHERMIC)
4) A solid (PRECIPITATE) forms from two aqueous solutions
Dissolved in water
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Demo’s
What evidence is there that a chemical
reaction has occurred?
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Representing
Chemical Reactions
In a chemical reaction, one or more substances change to
produce new substances.
• The starting materials are called REACTANTS and the
materials you finish with are called the PRODUCTS.
• A plus + sign is used between a list of different
reactants and products.
• An arrow  is used between the reactants and products
to show that the reactants get turned into the
products.
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Word Equations
A word equation describes a chemical reaction
using the names of the reactants and products.
Examples:
Hydrogen + Oxygen  water
Acetylene + oxygen  carbon dioxide + water
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Word Equations
A word equation describes a chemical reaction using the
names of the reactants and products.
Examples:
Hydrogen + Oxygen  water
Reactants
Products
Acetylene + oxygen  carbon dioxide + water
Reactants
Products
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Practice
Write word equations for the following descriptions. Underline the
Reactants and Circle the Products in each.
1) Aluminum metal combines with chlorine gas to make aluminum
chloride.
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Practice
Write word equations for the following descriptions. Underline the
Reactants and Circle the Products in each.
1) Aluminum metal combines with chlorine gas to make aluminum
chloride.
aluminum + chlorine  aluminum chloride
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Practice
Write word equations for the following descriptions. Underline the
Reactants and Circle the Products in each.
2) Magnesium metal combines with nitrogen gas to make magnesium
nitride.
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Practice
Write word equations for the following descriptions. Underline the
Reactants and Circle the Products in each.
2) Magnesium metal combines with nitrogen gas to make magnesium
nitride.
magnesium + nitrogen  magnesium nitride
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Practice
Write word equations for the following descriptions. Underline the
Reactants and Circle the Products in each.
3) Calcium chloride and sodium sulfide solutions are mixed. A
precipitate of calcium sulfide and sodium chloride solution is made.
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Practice
Write word equations for the following descriptions. Underline the
Reactants and Circle the Products in each.
3) Calcium chloride and sodium sulfide solutions are mixed. A
precipitate of calcium sulfide and sodium chloride solution is made.
Calcium chloride + sodium sulfide  calcium sulfide + sodium chloride
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Chemical Equations
A chemical equation is a short hand way of
representing a chemical change in which
chemical formulas are used for the reactants and
products.
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States for Substances
The states for the substances may be
included using the following symbols:
State Symbol
Meaning
(s)
Solid
(l)
liquid
(g)
gas
(aq)
aqueous
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Examples
H2 (g) + O2 (g)  H2O (l)
C2H2 (g)+ O2 (g)  CO2 (g) + H2O (l)
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Reminders
• Don’t forget the diatomic elements:
Hydrogen H2
Fluorine F2
Oxygen O2
Chlorine Cl2
Nitrogen N2
Bromine Br2
Iodine I2
Don’t forget to criss-cross the numbers in the ions to
make the subscripts in the compounds.
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Examples
Translate the following word equations into chemical
equations:
1) sodium + chlorine  sodium chloride
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Examples
Translate the following word equations into chemical
equations:
1) sodium + chlorine  sodium chloride
diatomic
Na+ Cl-
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Examples
Translate the following word equations into chemical
equations:
1) sodium + chlorine  sodium chloride
diatomic
Na+ Cl-
Na
+
Cl2

NaCl
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Examples
Translate the following word equations into chemical equations:
2) fluorine + calcium bromide  bromine + calcium fluoride
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Examples
Translate the following word equations into chemical equations:
2) fluorine + calcium bromide  bromine + calcium fluoride
diatomic
diatomic
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Examples
Translate the following word equations into chemical equations:
2) fluorine + calcium bromide  bromine + calcium fluoride
diatomic
Ca2+ Br-
diatomic
Ca2+ F-
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Examples
Translate the following word equations into chemical equations:
2) fluorine + calcium bromide  bromine + calcium fluoride
diatomic
F2
Ca2+ Br-
+ CaBr2
diatomic

Ca2+ F-
Br2 + CaF2
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Examples
Translate the following word equations into chemical equations:
3) barium sulfide + potassium iodide  barium iodide + potassium sulfide
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Examples
Translate the following word equations into chemical equations:
3) barium sulfide + potassium iodide  barium iodide + potassium sulfide
Ba2+ S2-
K+ I-
Ba2+ I-
K+ S2-
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Examples
Translate the following word equations into chemical equations:
3) barium sulfide + potassium iodide  barium iodide + potassium sulfide
Ba2+ S2-
BaS
K+ I-
+
KI
Ba2+ I-

BaI2
K+ S2-
+
K2S