Chemical Reactions
• Chemical changes are occurring
around us all the time
– Food cooking
– Fuel being burned in a car’s engine
– Oxygen being used in the human body
Chemical Reactions
• The starting materials are called
reactants
• The ending materials are called
products
Chemical Reactions
• To describe the reaction that creates
fire at the bunsen burner in lab
– Methane gas reacts quickly with oxygen
gas to produce fire, carbon dioxide, and
water vapor
– That’s a lot to write!
Chemical Reactions
• We can simplify the description of
our reaction by using a word
equation
Methane gas + oxygen gas →
fire + carbon dioxide gas + water vapor
• Still a lot to write!
Chemical Reactions
• There is an even simpler way to
express a chemical reaction
• We use formula equations to show
the reaction
Methane gas + oxygen gas →
fire + carbon dioxide gas + water vapor
CH4 + O2 → CO2 + H2O
– + represents “and”
– → represents “yields”
Chemical Reactions
Methane gas + oxygen gas →
fire + carbon dioxide gas + water vapor
CH4 + O2 → CO2 + H2O
• However there is some information
that is not shown in the formula
equation
– State of matter
– Fire/ Energy
Chemical Reactions
• We can show state of matter using the
following symbols
–
–
–
–
(s)
solid
(l)
liquid
(g)
gas
(aq) aqueous solution (substance is
dissolved in water)
Methane gas + oxygen gas →
fire + carbon dioxide gas + water vapor
CH4 (g)+ O2 (g) → CO2 (g) + H2O (g)
Chemical Reactions
• We can indicate if energy was
present in the reaction
– Reactions that have energy as a
reactant are called endothermic
• They require energy for the reaction to
occur
• Also sometimes represented as → or →
Heat
– Reactions that have energy as a product
are called exothermic
• Energy happens as a result of the reaction
Chemical Reactions
Methane gas + oxygen gas →
fire + carbon dioxide gas + water vapor
CH4 (g)+ O2 (g) → CO2 (g) + H2O (g) + energy
Chemical Reactions
Hydrogen plus oxygen yields water.
Nitrogen plus hydrogen yields ammonia.
Aluminum bromide plus chlorine yields
aluminum chloride and bromine.
Chemical Reactions
Hydrochloric acid plus sodium hydroxide
yields sodium chloride plus water.
Iron plus lead (II) sulfate react forming iron
(II) sulfate and lead.
Potassium chlorate when heated produces
potassium chloride plus oxygen gas.
Chemical Reactions
Sulfuric acid decomposes to form sulfur
trioxide gas plus water.
Sodium oxide combines with water to make
sodium hydroxide.
Potassium iodide reacts with bromine
forming potassium bromide plus iodine.
Chemical Reactions
Sodium phosphate reacts with calcium
nitrate to produce sodium nitrate and
calcium phosphate.
Zinc reacts with iron (III) chloride yielding
zinc chloride plus iron precipitate.
Ammonium carbonate and magnesium
sulfate react to yield ammonium sulfate
plus magnesium carbonate.
Chemical Reactions
Phosphoric acid plus calcium hydroxide react
forming solid calcium phosphate plus
water.
Aluminum plus oxygen form aluminum oxide
under certain conditions.
Nitrogen plus oxygen gas react and form
dinitrogen pentoxide.
Chemical Reactions
• The five general types of reactions:
–
–
–
–
–
Synthesis
Decomposition
Single-replacement
Double-replacement
Combustion
Chemical Reactions
• A synthesis reaction is a chemical
change in which two or more
substances react to form a single
new substance.
A + B → AB
2Mg + O2 → 2 MgO
Chemical Reactions
• A decomposition reaction is a
chemical change in which a single
compound breaks down into two or
more simpler products
AB → A + B
2NaN3 → 2Na + 3N2
Chemical Reactions
• A single-replacement reaction is
one in which one element replaces
a second element in a compound
AB + C → AC + B
2NaCl + Br2 → 2NaBr + Cl2
or
C + AB → A + CB
Zn + Cu(NO3)2 → Cu + Zn(NO3)2
Chemical Reactions
• A double-replacement reaction
which is a chemical change
involving an exchange of positive
ions between two compounds.
AB + CD → AD + CB
2NaNO3 + CuBr2 → 2NaBr +Cu(NO3)2
Chemical Reactions
• A combustion reaction is a chemical
change in which an element or a
compound reacts with oxygen,
often producing energy in the form
of heat and light.
CH4 +
2O2
→ CO2 + 2H2O