1. Chemical Reactions
Chapter 23

2. Chemical Reactions Chemical reactions are happening all around you
A chemical reaction is a change in which one or more substance become new substances
In all chemical reactions, the mass of the starting reactants equals the total mass of all products
What is this law called?
The Law of Conservation of Mass

3. Writing Equations
A chemical equation is a way to describe a chemical reaction using chemical formulas and other symbols
On the left side of the equation are the reactants
On the right side of the equation are the products
Other symbols are also included to provide more information about the reactants, products, and reaction conditions
Symbol
Meaning 
Produces or yields +
Plus
(s)
Solid
(l)
Liquid
(g)
Gas
(aq)
Aqueous

4. Coefficients Remember:
Matter can not be created or destroyed in reactions
There will be the same number of each type of atom on both sides of the equation
This is done by using coefficients
These are the numbers found in front of each compound

5. Balancing Equations
An equation will need to be balanced to ensure that the same number of atoms of each element are on both sides of the equation
This is done by assigning coefficients

6. Steps for Balancing equations
Step 1: Write the equation
Step 2: Count the atoms of each element in both the reactants and the products
Step 3: Choose the coefficients necessary to balance the equation
Step 4: Recheck your answer

7. types of REactions Combustion Reactions Synthesis Reactions
A substance reacts with oxygen to produce energy in the form of heat and light
Synthesis Reactions
Two or more substances combine to from another substance
Decomposition Reactions
A substance breaks down into two or more substance

8. Types of REactions Single Displacement Double Displacement
One compound replaces another in a compound
Double Displacement
Two ionic compounds separate into ions and then reform to form two new ionic compounds
The ions flip-flop
Oxidation-Reduction Reaction
Reaction where one reactant loses electron(s) and the other gains electron(s)
The one losing electrons is oxidized
The one gaining electrons is reduced

9. Energy and Chemical Reactions
In some reactions, energy is needed to make the reaction happen
Energy will be absorbed as heat or light
They are endothermic
The reaction will feel cool to the touch
In other reactions, energy will be released when the reaction occurs
Energy will be released as heat or light
They are exothermic
The reaction will feel warm to the touch
Endergonic Reactions
Exergonic Reactions

10. Energy and Chemical Reactions