Types of Chemical Reactions

States

From this point forward, all components of a chemical reaction will need to show the state

There are 4 states

1. Solid

2. Liquid

3. Gaseous

4. Aqueous – Dissolved in water

An Aqueous substance will be ionic and is actually the ions separated from each other by water

Types of Chemical Reactions

There are only five (5) different types of chemical reactions: 1) Double Replacement

2) Single Replacement

3) Synthesis/Formation

4) Decomposition

5) Combustion

Reaction Type 1 – Double Replacement

Occur between two ionic compounds Does not happen with covalent compounds

Involves an exchange of cations (positive ions)

The cation of one compound trades places with the cation of another compound to form two new compounds

Double Replacement - Characteristics

occur in solution when the compounds are in an aqueous state (aq) reactants are either aqueous to begin with, or

solid compounds dissolved in water to form an aqueous solution of ions

in order to drive the reaction, one of the products must be removed from the aqueous solution

this can occur via one of three ways:

Double Replacement - Characteristics

1) Formation of a precipitate (an insoluble solid forms in the solution)

i.e.:

AgNO3 (aq) + NaCl (aq) NaNO3 (aq) + AgCl (s)

Solid silver chloride is formed as precipitate and comes out of the solution

Double Replacement - Characteristics

2) Formation of a gas

i.e.:

FeS (aq) + 2HCl (aq) H2S (g) + FeCl2 (aq)

Hydrogen sulfide gas is formed and comes out of the solution

Double Replacement - Characteristics

3) Water is formed when a hydrogen cation unites with a hydroxide anion

i.e.:

NaOH (aq) + HCl (aq) HOH (l) + NaCl (aq)

Water (HOH) is formed and comes out of the solution

Determining if a Double Replacement Reaction Occurs & Predicting the States of the Products

1) Formation of a Precipitate Use a “Solubility Table”

Look at the compounds formed, and use a solubility table to identify if a precipitate is formed

If a precipitate is formed, it will be written as a solid in the products

If no precipitate forms, the reaction will not occur. You will simply have a mixture of ions

Determining if a Double Replacement Reaction Occurs & Predicting the States of the Products

2) Formation of a gas

Solubility table is not helpful

More difficult to identify

Use your best judgment, or the info will be given in the question

3) Formation of water

If water is a product, it will be written as a “liquid”, not “aqueous” since it is a pure liquid

Yes, water is technically a covalent compound, however it is still present in double replacement reactions.

Sometimes it is helpful to write H2O as HOH symbolizing the joining of a H+ cation and an OH- anion

Identifying a Double Replacement Reaction

Double replacement reactions always have two ionic compounds on the REACTANTS side AND on the PRODUCTS side of an equation

*Two compounds react to form two new compounds* AB + CD CB + AD

A & C are cations, B & D are anions

A & C switch places

Reaction Type # 2 – Single Replacement

Single Replacement Reactions: Characteristics:

Atom (s) of a lone element replace the atom (s) of an element in a compound Metals replace metals (or cations replace cations)

Non-metals replace non-metals (or anions replace anions)

Single Replacement Reactions: Characteristics:

Metal Cation Replacement: For the reaction:

A + BC B + AC

A and B are cations A “replaces” B in the compound

Single Replacement Reactions: Characteristics:

Non-metal Anion Replacement: For the reaction:

D + EF ED + F

D & F are anions D “replaces” F in the compound Non metal replacements usually involve

halogens

Single Replacement Reactions

Restrictions on Single Replacement Reactions

Activity Series: A characteristic of metals and halogens

referring to their reactivity Determines whether or not a single

replacement reaction will occur or not Metals: on page 155 (table 7-2) there is

an activity series of metals arranged in order of decreasing activity

Non-metals (Halogens) : as you move down the group on the periodic table activity decreases

Restrictions on Single Replacement Reactions

A single replacement reaction WILL NOT OCCUR if the reactivity of the pure element reactant is less than that of the compound reactant i.e.:

Sn (s) + NaNO3 (aq)

no reaction b/c tin is less reactive than sodium

Restrictions on Single Replacement Reactions

A single replacement reaction WILL OCCUR if the reactivity of the pure element reactant is greater than that of the compound reactant i.e.:

Zn (s) + H2SO4 (aq) ZnSO4 (aq) + H2 (g)

Reaction occurs because the reactivity of zinc is higher than hydrogen

Identifying Single Replacement Reactions

Single replacement reactions ALWAYS have 1 lone element and 1 compound on the reactants side and the products side

Reactants will always be: 1 lone element + 1 compound

Products will always be: 1 lone element + 1 compound