Reaction Notes.notebook
March 02, 2016
Physical change: a change is a substance that does not change the identity
(composition) of the substance; a change in size, shape, mass, volume,
phase, etc.
Phase changes:
Melting: solid à liquid
Freezing: liquid à solid
absorbs energy, +E
releases energy, ‐E
Vaporization: liquid à gas
Condensation: gas à liquid
absorbs energy, +E (boiling)
releases energy, ‐E
Sublimation: solid à gas
Deposition: gas à solid
absorbs energy, +E (dry ice)
releases energy, ‐E (frost)
Mar 2­8:39 AM
Chemical change: a change in which a substance undergoes a change in
identity (composition); burning, rusting, decomposing, etc
Indicators of a chemical change
Heat, light or sound are produced
A change in odor or color
A precipitate or gas forms when two solutions are mixed
Mar 2­8:42 AM
Reaction Notes.notebook
March 02, 2016
Symbol or term
Explanation
Reactants
Starting substances
A + Bà C + D
Products
Substances formed
A + Bà C + D
à
yields, produces
⇌
reversible reaction, equilibrium
(s)
Solid
(l)
Liquid
(g)
Gas
(aq)
aqueous (dissolved in water)
coefficient
subscript
number in front of a substance that
indicates moles or units
number in a formula that indicates
# of atoms (or polyatomic ions)
∆
heat is used in a reaction
catalyst
a catalyst is used to lower
activation energy
exothermic
the reaction releases energy
endothermic
the reaction absorbs energy
activation energy
the energy needed to start or
initiate a reaction
Mar 2­8:43 AM
Balancing equations
Law of Conservation of Mass: every balanced equation must satisfy the
‘LCM’. The total mass of the reactants must equal the total mass of
the products. The number of atoms of each element must be the same
on both sides of the equation.
When balancing chemical equations, only the coefficients can be
changed. Never change the subscripts. Changing the coefficients
changes the number of units of the substance. Changing the
subscripts changes the identity of the substance.
As a general rule:
Balance polyatomic ions first, if present. Then balance other
anions.
Balance metals next.
Balance H and O last.
Mar 2­8:45 AM
Reaction Notes.notebook
March 02, 2016
Synthesis reaction (combination, direct combination)
Two or more reactants combine to form one product
General form: A + B --> AB
Example: 2H2(g) + O2(g) --> 2H2O(g)
Mar 2­8:46 AM
Decomposition reaction (analysis)
One reactant breaks down into two or more
simpler products. Most are endothermic, using
heat or electricity for decomposition.
General form: AB --> A + B
Example: 2H2O(l) --> 2H2(g) + O2(g)
Mar 2­8:50 AM
Reaction Notes.notebook
March 02, 2016
Single replacement reaction (single displacement)
A free element replaces an element in a compound. The
free element must be more active than the element in the
compound. Use the activity series to determine which
element is more active. Use the activity series to
determine whether the reaction will occur.
General form: A + BC --> AC + B
Example:
metal
Cu(s) + 2AgNO3(aq)
metal
--> Cu(NO3)2(aq) + 2Ag(s)
D + BC --> BD + C
nonmetal
nonmetal
Example: Cl2(g) + 2NaBr(aq) --> 2NaCl(aq) + Br2(g)
Mar 2­8:50 AM
Double replacement reaction (double displacement)
Occurs in an aqueous solution. Only occurs if one of the
following are produced: a precipitate, a gas, or water.
Use solubility rules to identify precipitates; precipitates
are insoluble in water.
General form: AB + CD --> AD + CB
Example: K2SO4(aq) + CaCl2(aq) --> 2KCl(aq) + CaSO4(s)
Mar 2­8:50 AM
Reaction Notes.notebook
March 02, 2016
Combustion reaction (burning)
Oxygen is always a reactant, carbon dioxide and
water are always products.
General form: CxHy + O2 --> CO2 + H2O
Example: C3H8(g) + 5O2(g) --> 3CO2(g) + 4H2O(l)
Mar 2­8:50 AM
Predicting Products
Use the activity series (on your reference tables) to predict
whether or not a single replacement reaction will occur. If
the free element is more active (higher up) than the
element in the compound, then the reaction will occur. If
the free element is less active (lower down) than the
element in the compound, then the reaction will not occur.
Single replacement reactions are not reversible.
In order for a double replacement reaction to occur, one
product must be a gas, water, or a precipitate. Use the
solubility rules (on your reference tables) to predict
precipitates. Remember (aq) means soluble, dissolves in
water; (s) means solid, indicating insoluble, does not
dissolve in water. If all products are aqueous, then no
reaction has occurred!
Mar 2­8:56 AM
Reaction Notes.notebook
March 02, 2016
Writing Ionic and Net Ionic Equations (for double replacement only!)
Aqueous ionic compounds can be separated into ions (don’t forget to
include charges!)
Strong acids and bases can be separated into ions.
Substances that are solids (s), liquids (l), or gases (g) cannot be separated!
Ions that show up on both sides of the balanced equation are spectator
ions.
Spectator ions can be removed from the ionic equation leaving a net ionic
equation.
Example:
Na2SO4(aq) + BaCl2(aq) --> 2NaCl(aq) + BaSO4(s)
ionic equation:
2Na1+ + SO42‐ + Ba2+ + 2Cl1‐ --> 2Na1+ + 2Cl1‐ + BaSO4(s)
spectator ions:
Na1+, Cl1‐
net ionic equation:
SO42‐(aq) + Ba2+(aq) --> BaSO4(s)
Mar 2­8:59 AM
Mar 2­8:59 AM
Reaction Notes.notebook
March 02, 2016
Mar 2­8:59 AM