Chemical Reactions

Combination Reactions, Single Replacement Reactions, Combustion Reactions, Decomposition Reactions, Double Displacement Reactions,

Precipitation Reactions, Neutralization Reactions, Gas Forming Reactions

Chemical Reactions During a chemical reaction both the form and composition of matter are

changed. 

Old substances are converted to new substances, which have unique physical and chemical properties of their own. 

Some of the observable signs that a chemical reaction has occurred include the following:

 • A metallic deposit appears• Bubbles appear• A temperature change occurs• A color change occurs• A precipitate (cloudy, tiny particles) appears

   

Types of Chemical Reactions

Combination Reactions

Single Replacement Reactions

Combustion Reactions

Decomposition Reactions

Double Replacement Reactions   

Combination Reaction A combination reaction is a chemical change in which two or more substances

react to form a single new substance..

All combination reactions have the general form: 

A  +  B  C 

For example;Sodium + Chlorine

The predicted product is sodium chloride.

Reaction equation: 2Na (s) + Cl2→ 2NaCl (s)

Single Replacement Reaction A single-replacement reaction is a chemical change in which one element

replaces a second element in a compound.

All single displacement reactions have the general form: 

A  +  BC  B  +  AC

For example;Zinc metal + aqueous copper nitrate

The predicted products are the element Cu and the compound Zn(NO3)2.

Reaction equation: Zn (s) + Cu(NO3)2 (aq) → Cu(s) + Zn(NO3)2 (aq)

Combustion Reaction A combustion reaction occurs when an element or a compound reacts with

oxygen, often producing energy in the form of heat and/or light.

A combustion reaction always involves oxygen as a reactant.

Often the other reactant is a hydrocarbon producing carbon dioxide, water and a large release of energy as heat.

Explains why hydrocarbons such as methane (CH4), propane (C3H8), and butane (C4H10) are important fuels.

For example;Methane + Oxygen

The predicted products are the element carbon dioxide and water.

Reaction equation: CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g)

Decomposition Reaction A decomposition reaction is a chemical change in which a single compound

breaks down into two or more simpler products.

Decomposition reactions involve only one reactant and two or more products.

All decomposition reactions have the general form: 

AB   A  +  B

For example;mercury oxide + energy (heat, light or electricity)

The predicted products are the element mercury and oxygen.

Reaction equation: HgO (s) → Hg (l) + O2 (g)

Double Replacement Reactions  All double replacement reactions have the general form: 

AB  +  CD  AD  +  CB

Reactions that can be classified as double replacements include precipitation reactions, neutralization reactions and gas forming reactions.

• Precipitation Reactions

• Neutralization Reactions

• Gas Forming Reactions

Precipitation Reactions AB and CD are usually aqueous ionic compounds consisting of aqueous ions:

(A+ and B-, C+ and D-). 

In a double replacement reaction, the cations and anions switch partners, resulting in the formation of two new ionic compounds AD and CB, one of which is in the solid state.

For Example;aqueous lead(II) nitrate + aqueous sodium chloride                                                            The predicted products are lead(II) chloride (insoluble) and sodium nitrate (soluble).  Since one of the predicted products is insoluble, a precipitation reaction has occurred.                                                                                                Reaction Equation:  Pb(NO3)2 (aq) + 2 NaCl (aq) → 2 NaNO3 (aq) + PbCl2 (s)

Neutralization Reactions AB is an acid (consisting of H+ and X- aqueous ions) and BC is a base

(consisting of M+ and OH- ions). 

When a double replacement neutralization reaction occurs, the cations and anions switch partners, resulting in the formation of water and a new ionic compound (or salt), which is usually soluble. 

Neutralization reactions are exothermic, and are generally accompanied by a noticeable release of heat.

For example;

sulfuric acid + aqueous lithium hydroxide 

The predicted products are water and lithium sulfate.                                                                                                 

Reaction Equation:  H2SO4 (aq) + 2 LiOH (aq) → Li2SO4 (aq) + 2 H2O (l)

Gas Forming Reactions In a gas forming double replacement reactions, one of the products (AD or

CB) is in the gaseous state, such as carbon dioxide (CO2). 

For example;

Hydrochloric acid + aqueous sodium bicarbonate           

The predicted products are carbon dioxide and sodium chloride. 

Reaction Equation: HCl (aq) + NaHCO3 (aq)  →  H2O (l) + CO2 (g)  

SOLUBILITY RULES 1.      Alkali metal compounds, acetates, nitrates, and ammonium compounds are all soluble.   2.      Hydroxides of alkali metals and NH4

+1, Ca+2, Sr+2, and Ba+2 are soluble.  All others are insoluble.

 3.      All halides (chlorides etc.) are soluble except for those containing Ag+1, Pb+2, and Hg2

+2. 4.      Most sulfates are soluble, except for BaSO4, SrSO4, Ag2SO4, PbSO4, and CaSO4. 5.      Most phosphates, carbonates, chromates and sulfides are insoluble (except those of the

alkali metals and ammonium).   6.      All acids are soluble. 

SOLUBILITY CURVE The solubility curve traces the solubility

of a substance over a range of temperatures.

The solubility curve helps identify a known solution as saturated or unsaturated.

To find the least soluble substance at a given temperature we follow the temperature line up and the first substance curve we cross is the least soluble.

For most soluble it is the same procedure except the last substance curve crossed is the most soluble.

SOLUBILITY CURVE

1. Which salt is least soluble at 20oC?

KClO3

2. Which salt is most soluble at 20oC?

KI

3. At 40oC how much KNO3 can be dissolved in 100g of H2O?

      about 64g KNO3