Rapid Review
Reactions will always occur in the free-response section of the AP exam. This may not
be true in the multiple-choice part.
Energy may be released in a reaction (exothermic) or absorbed (endothermic). Chemical equations are balanced by adding coefficients in front of the chemical species
until the number of each type of atom is the same on both the right and left sides of the
arrow.
The coefficients in the balanced equation must be in the lowest whole-number ratio. Water is the universal solvent, dissolving a wide variety of both ionic and polar substances. Electrolytes are substances that conduct an electrical current when dissolved in water;
nonelectrolytes do not.
Most ions in solution attract and bind a layer of water molecules in a process called
solvation.
Some molecular compounds, like acids, ionize in water, forming ions. In the molecular equation, the reactants and products are shown in their
undissociated/unionized form; the ionic equation shows the strong electrolytes in the
form of ions; the net ionic equation drops out all spectator ions and shows only those
species that are undergoing chemical change.
Precipitation reactions form an insoluble compound, a precipitate, from the mixing of
two soluble compounds.
Learn and be able to apply the solubility rules. Redox reactions are reactions where oxidation and reduction take place simultaneously. Oxidation is the loss of electrons and reduction is the gain of electrons. Oxidizing agents are reactants that cause oxidation to take place (the reactant being
reduced), and reducing agents are reactant species that cause reduction to take place
(the reactant being oxidized).
Combination reactions are usually redox reactions in which two or more reactants
(elements or compounds) combine to form one product.
Decomposition reactions are usually redox reactions in which a compound breaks down
into two or more simpler substances.
Single displacement reactions are redox reactions in which atoms of an element replace
the atoms of another element in a compound.
Know how to use the activity series to predict whether or not an element will displace
another element.
Combustion reactions are redox reactions in which the chemical species rapidly
combine with diatomic oxygen gas, emitting heat and light. The products of the com-
plete combustion of a hydrocarbon are carbon dioxide and water.
Indicators are substances that exhibit different colors under acidic or basic conditions. Acids are proton donors (electron-pair acceptors).86 STEP 4. Review the Knowledge You Need to Score High