General Aspects of Chemical Reactions and Equations

Balancing Chemical Equations

• Law of Conservation of Matter, which says that in ordinary chemical reactions matter is neither created nor destroyed.

• Balancing the chemical equation shows which chemical species are the reactants and which species are the products. It may also indicate in which state of matter the reactants and products exist.

• The number of each type of reactant atom has to equal the number of each type of product atom.

Periodic relationships

• Bonding is that nonmetals react with other nonmetals to form covalent compounds, and that metals react with nonmetals to form ionic compounds.

• If the reaction that is producing the ionic compound is occurring in solution, you will be expected to write the net ionic equation for the reaction.

General Properties of Aqueous Solutions

• Water is called the universal solvent, because it dissolves so many substances.

• Ionic compounds that dissolve in water (dissociate) form electrolyte solutions, which conduct electrical current owing to the presence of ions.

• ions can attract the polar water molecules and form a bound layer of water molecules around themselves. This process is called solvation.

• nonelectrolytes—substances that do not conduct an electrical current when dissolved in water.

• certain covalent compounds, like acids, will ionize in water,

• molecular equation, in which both the reactant and products are shown in the undissociated form:

Pb(NO ) (aq) N+ → a SO (aq) PbSO (s)+ 2NaNO (aq)

• Ions which are not actually involved in the chemical reaction taking places are called spectator ions.

• The net ionic equation is written by dropping out the spectator ions and showing only those chemical species that are involved in the chemical reaction:

Pb + − (aq)+ → SO (aq) PbSO (s)

Precipitation Reactions

• Precipitation reactions involve the formation of an insoluble compound, a precipitate, from the mixing of two soluble compounds.

• If at least one insoluble product is formed, the reaction is classified as a double displacement (replacement) or metathesis reaction.

Oxidation–Reduction Reactions

• Oxidation–reduction reactions, also called redox reactions

• The driving force involved in redox reactions is the exchange of electrons from a more active species to a less active one.

• Redox is a term that stands for reduction and oxidation. Reduction is the gain of electrons, and oxidation is the loss of electrons.

Combination Reactions

• Combination reactions are reactions in which two or more reactants combine to form one product.

Decomposition Reactions

• Decomposition reactions are reactions in which a compound breaks down into two or more simpler substances

• electrolysis, in which an electrical current is used to decompose a compound into its elements:

Single Displacement Reactions

• Single displacement (replacement) reactions are reactions in which atoms of an element replace the atoms of another element in a compound.

Combustion Reactions

• Combustion reactions are redox reactions in which the chemical species rapidly combines with oxygen and usually emits heat and light.

Coordination Compounds

• A complex ion is composed of a metal ion bonded to two or more molecules or ions called ligands.

• In reactions involving coordination compounds, the metal acts as the Lewis acid, while the ligand acts as a Lewis base

• The coordination number is the number of donor atoms that surround the central atom.

Acid–Base Reactions

Properties of Acids, Bases, and Salts

• acids are defined as proton donors or electron-pair acceptors. Bases are defined as proton acceptors or electron-pair donors

• Coordinate covalent bonds are covalent bonds in which one of the atoms furnishes both of the electrons for the bond.

• Acids and bases may be strong, dissociating completely, or weak, partially dissociating and forming an equilibrium system

Acid-Base Reactions

• acids react with bases to form a salt and, usually, water.

• Reactions of this type are called neutralization reactions.

Acid–Base Titrations

• A titration is a laboratory procedure in which a solution of known concentration is used to determine the concentration of an unknown solution.

• The equivalence point is that point in the titration where the number of moles of H+ in the acid solution has been exactly neutralized with the same number of moles of OH-

Common Mistakes to Avoid

1. In balancing chemical equations don’t change the subscripts in the chemical formula,

just the coefficients.

2. Molecular compounds ionize, ionic compounds dissociate.

3. In writing ionic and net ionic equations, show the chemical