Download AP Reaction Rules

AP Chemistry Reaction Rules
Double Replacement = 2 compounds yield 2 different compounds
(only occurs if water, a gas, or a precipitate is formed)
The oxidation number of the metal stays the same from reactant to product
Single Replacement = 1 element and 1 compound yield 1 different element and 1 different compound
(only occurs if replacing element is below replaced element in the reduction potential list)
Use the preferred oxidation number for the metal/nonmetal and watch for diatomic elements
Combination (also called Synthesis) = 2 or more substances yield only 1 compound
A. Formation of a Binary Compound
2 elements yield 1 binary compound - Use the preferred oxidation numbers for the metal/nonmetal and watch for diatomic elements
B. Formation of an Oxyacid (H with polyatomic ion containing oxygen)
Nonmetallic oxide and water yield an oxyacid
Use NOTE 1 below to determine if the polyatomic ion is “ate” or “ite”
C. Formation of a Base (metal with hydroxide)
Metallic oxide and water yield a base
The oxidation number of the metal stays the same from reactant to product
D. Formation of an Oxysalt (metal with polyatomic ion containing oxygen)
Nonmetallic oxide and metallic oxide yield an oxysalt
Metal retains the oxidation number from oxide, use NOTE 1 below to determine if the polyatomic ion is “ate” or “ite”
Decomposition = 1 compound yields 2 or more simpler substances
A. Decomposition of a Binary Compound
1 binary compound yields two elements
Watch for diatomic elements
B. Decomposition of an Oxyacid (H with polyatomic ion containing oxygen)
Oxyacid yields nonmetallic oxide and water
Reverse NOTE 1 below to determine valence on nonmetal
C. Decomposition of a Base (metal with hydroxide)
Base yields metallic oxide and water
Metal retains the oxidation number from its base form
D. Decomposition of an Oxysalt (metal with polyatomic ion containing oxygen)
Oxysalt yields nonmetallic oxide and metallic oxide
Metal retains the oxidation number from oxysalt, reverse NOTE 1 below for the valence on the nonmetal
NOTE 1: High valence on the nonmetal ↔ “ate” radical, Low valence on the nonmetal ↔ “ite” radical
Combustion: oxygen needed as a reactant (do not confuse with “heated”)
For a hydrocarbon, products are carbon dioxide and water
For an element, it is a combination reaction
Acid-Base Neutralization: works like a double replacement reaction
Acid
Base
Arrhenius
Proton (H+) donor
Hydroxide donor
Bronsted-Lowry
Proton (H+) donor
Proton (H+) acceptor
Lewis
Electron pair acceptor
Electron pair donor
For Arrhenius definition, products are water and a salt
For Bronsted-Lowry definition, products are a weak base and weak acid
(For Lewis definition, product is a single compound – combination reaction, see complex ion)
Complex Ion Formation: a substrate gets surrounded by ligands
Substrate is electron-deficient (Lewis acid) – like BF3 or transition metal
Ligands are electron rich (Lewis base) – like NH3 or negative polyatomic ion
Typically there is an excess of ligands (“excess”, large volume of “concentrated”)
Typically twice the number of ligands will attach as the charge on the Lewis acid
Redox: a change in the oxidation number of one or more reactants occurs as products are formed
Include single replacement, combination, and decomposition reactions
Oxidation numbers are a book-keeping idea, not the same as a “charge”, but might match
Oxidation is loss of electrons, so oxidation numbers positively increase
Reduction is gain of electrons, so oxidation numbers negatively reduce
Basic rules for assigning oxidation numbers (follow this order!):
1) All elements in their natural state have an oxidation number = 0
2) fluoride = -1 (always)
3) oxide = -2 (exceptions are peroxides, superoxides, and with fluoride)
4) hydrogen = +1, hydride = -1
5) the sum of the elements’ oxidation numbers must equal the charge on the compound/polyatomic ion, or zero if there is no charge
Net ionic equation: show soluble compounds and strong acids/bases as ions, spectator ions are removed
Should be written for all reaction types, and are mandatory on the AP test
Soluble ionic compounds and strong acids/bases must be ionized (use solubility rules)
Precipitates (solids), gases, water, and weak acids/bases should not be shown as ionized
Spectator ions (exactly the same on both sides of the arrow) should be removed