1. Chemical Reactions

2. Chemical reactions occur in our world constantly
The explosion of dynamite, the reaction of household cleaners and the rusting of iron are all examples of chemical reactions

3. Sometimes the chemical reaction is quite simple to explain, where are in other situation it is very complicated
Just like we saw patterns in how chemical compounds are organized we will learn to recognize patterns that will help us to understand and predict different kinds of chemical reactions

4. Word Equations
A word equation is one way of representing a chemical reaction: it tells you what reacts and what is produced
Word equations are:
An efficient way to describe chemical reactions
Help chemists recognize patterns to predict the products of chemical reactions

5. Word equations are written in a certain format:
All the reactants All the products
*** the arrow always points from reactant to products ***
Reactants – substances present initially
Products – substances present at the end

6. Ex: When we combine iron and oxygen we get iron(III) oxide.
If we place a coil of copper wire in a beaker of colorless silver nitrate we get the following reaction:

7. Balancing Chemical Equations
We can also describe the chemical reactions using symbols
Ex. Methane burns in air by reacting with oxygen to produce water and carbon dioxide

8. Law of conservation of mass
States that the mass of the reactants in any chemical reaction must equal the mass of the products
In other words atoms cannot be created or destroyed in a chemical change
Therefore we must look at the reactants and products and record the number of atoms of each type of element

9. An equation in which the reactants and the products contains equal numbers of atoms of each type of element is a balanced equation.
The usual way to write balanced equations is to use a coefficient.
The coefficient indicates the number of atoms or molecules of that substance.

10. How to balance an equation
Step 1 –write the word equation for the reaction
Iron + oxygen magnetic iron oxide
Step 2 – write the skeleton equation by replacing each name with a correct formula
Step 3 – count the number of atoms of each type in the reactants and products

11. Step 4 – multiply each of the formulas by the appropriate coefficient to balance the number of atoms

12. Balance the following:
Magnesium + nitric acid hydrogen + magnesium nitrate