CHEM Ch.5 Balancing Chemical Reactions

Step #2 to Balancing Chemical Equations

Add appropriate coefficients to balance the numbers of atoms of each element.

Non-Soluble Anionic Compounds

Ag+ Hg2 2+ Pb 2+ Ba 2+ Hg2 2+ Pb 2+

Oxidation Number Rule #1

An atom in its elemental state has an oxidation number of zero.

Ionic Equation

An equation in which ions are explicitly shown.

Chemical Equation

An expression in which symbols and formulas are used to represent a chemical reaction.

Precipitate

An insoluble solid that forms in solution during a chemical reaction.

Salt

An ionic compound formed from reaction of an acid with a base.

Acid-Base Neutralization Reaction Example

Another kind of neutralization reaction occurs between an acid and a carbonate (or bicarbonate) to yield water, a salt, and a carbon dioxide. The reaction occurs because the carbonate ion (CO3 2-) reacts initially with H+ to yield H2CO3, which is unstable and immediately decomposes to give CO2 + H2O

Recognizing Redox Reactions

Atoms involved are metals & nonmetals

Step #3 to Balancing Chemical Equations

Check the equation to make sure the numbers and kinds of atoms on both sides of the equation are the same.

Balanced Equation

A chemical equation in which the numbers and the kinds of atoms are the same on both sides of the reaction arrow.

Oxidation Number Rule #2

A monatomic ion has an oxidation number equal to its charge.

Coefficient

A number placed in front of a formula to balance a chemical equation.

Balancing Chemical Equations

A polyatomic ion appears on both sides of an equation, it is treated as a single unit. For example, sulfate ion (SO4 2-). H & O are balanced last.

Oxidation-Reduction (Redox) Reaction

A reaction in which electrons are transferred between reaction partners (atoms, molecules, or ions).

General Rule #2 on Solubility

Cl- Br- I- NO3 - ClO4 - CH3CO2 - SO4 2-

Oxidation Reduction Reaction Example

Copper metal gives electron to each of the 2 Ag+ ions, forming Cu 2+ and silver metal. Copper is oxidized in the process, and Ag+ is reduced.

How to calculate Oxidation Number

Ex. Oxidation Number for Cr in CO

How to calculate Oxidation Number

Ex. Oxidation Number for Mn in KMnO4

Reduction

Gaining electrons

Oxidizing Agent

Gains one or more electrons Causes oxidation Undergoes reduction Becomes more negative (less positive) May lose oxygen atoms

Solubilities

How much of each compound will dissolve in a given amount of solvent at a given temperature. If a substance has a low solubility in water, then it is likely to precipitate from an aqueous solution. if a substance has a high solubility in water, then no precipitate will form .

Oxygen Atoms in Redox Reactions

If an atom gains oxygen it will make the atom oxidized after the reaction. If an atom loses oxygen it will make the atom reduced after the reaction.

Oxidation Number Rule #3

In a molecular compound, an atom usually has the same oxidation number it would have if it were a monatomic ion.

Oxidation Number

Indication of which atom is neutral, electron-rich, or electron-poor. Does not necessarily imply ionic charges.

General Rule #1 on Solubility

Li+ Na+ K+ Rb+ Cs+ NH4 +

Reducing Agent

Loses one or more electrons Causes reduction Undergoes oxidation Becomes more positive (less negative) May gain oxygen atoms

Oxidation

Losing electrons

Step #4 to Balancing Chemical Equations

Make sure the coefficients are reduced to their lowest whole-number values.

Law of Conservation of Mass

Matter can neither be created nor destroyed in a chemical reaction. Bonds between atoms in the reactants are rearrange to form new compounds in a chemical reaction. None of the atoms disappear and no new ones are formed.

Precipitation Reactions

Occurs when anions and cations of two ionic compounds change partners.

Acid-Base Neutralization Reactions

Processes in which an acid reacts with a base to yield water plus an ionic compound called SALT. Note in the example that this reaction produced sodium chloride.

Oxidation Number Rule #4

The sum of the oxidation numbers in a neutral compound is zero.

Ionic Compounds

Undergo reactions in aqueous solution. Dissolved in water.

Example of Redox

When metallic magnesium reactions with iodine vapor, the magnesium atom gives an electron to each of the 2 iodine atoms, forming a Mg2+ ion and two I- ions. The charge on the magnesium changes from 0 to 2+, and the charge on each iodine changes from 0 to -1.

Step #1 to Balancing Chemical Equations

Write an unbalanced equation, using the correct formulas for all given reactants and products.