CHEM 1411 - General Chemistry I
Course Lecture Notes
Fall 2007
Instructor: Dr. Shawn Amorde
Chapter 4 Lecture Notes
web page: www.austincc.edu/samorde
Some Types of Chemical Reactions
Text Chapters (4.1-4.3, 4.7-4.13)
Recommended Problems: (20, 26, 30, 32, 42, 44, 48, 50, 58, 67, 68, 70, 74, 82, 90, 92, 96, 106, 114, 117-127)
I. Chemical Reactions
II Classifying Chemical Reactions
A. Oxidation-Reduction Reactions
B. Combination Reactions
C. Decompositions Reactions
D. Displacement Reactions
E. Metathesis Reactions
F. Gas-Forming Reactions
G. Summary
Reactions!!
There are three main forms to write many of these equations.
The first is the formula unit equation. This means we write the complete formula for each compound!!
The second is the total ionic equation, This means we can write each compound as its reacting ion.
The third is the net ionic equation. This is just the reacting ions.
Ionization Reactions
Compounds that are water soluble and separate into its ions in solution are said to dissociate upon dissolving, or undergo a dissociation reaction. Here’s an example.
Another dissociation reaction is the addition of HX, like HCl to water.
When the cation is H+ the reactant is an acid, and the solution is acidic!!
There are strong acids like HCl and weaker acids like HCN. What makes a strong acid, strong?
A weak acid, weak?
How about NaOH in water?
This is a strong base. When a compound dissociates to give –OH, the compound is a base and the solution is basic.
There are also strong and weak bases.
Remember the arrows on the reaction, they can mean different things….i.e. how strong is the reaction and is it reversible?
How do you get a reaction that is not reversible? Let us look at our Chloride Lab.
We formed a white ppt. (AgCl) this was insoluble in water and stopped reacting!!
Some solubility charts are on page 128.
Oxidation-Reduction
Reactions
Redox Reactions
Oxidation refers to increasing the oxidation number!! This means the atom is losing electrons!!
Reduction refers to reducing the oxidation number!! This means gaining electrons.
But, remember the oxidation number in a molecule must add up to zero….the same will be true for a reaction…….
This means, oxidation and reduction must both occur in the same reaction with equal but opposite oxidation states!!
Remember the big picture here, redox reactions are the exchange of electrons, we can not gain or lose the total number of electrons present, only move them around.
For example,
Let’s look at several examples.
Combination Reactions
Reactions in which two or more substances combine to form a compound are called combination reactions.
There are three main classes of these reactions;
Element/Element
Compound/Element
Compound/Compound
Decomposition reactions
These are reactions in which compounds break down into one or more elements and one or more compounds, or two or more compounds.
Essentially these are the reverse of combination reactions.
Element/Element
Compound/Element
Compound/Compound
Displacement Reactions
Reactions in which one element replaces another in a compound are called displacement reactions.
For example;
How can we predict if this will happen?
Active metals displace less active metals!! Consult the chart on page 146.
Metathesis Reactions
A reaction in which the anions “switch” cation partners.
For example,
An acid base reaction
often precipitation forming reactions
or gas forming reactions