1. BALANCING CHEMICAL EQUATIONS

2. Bell Ringer Question In your own words what is a chemical reaction?
Share your answers with the students sitting at your lab table.

3. What is a Chemical Reaction?
A chemical reaction is the process by which the atoms of one or more substances are rearranged to form different substances; occurrence can be indicated by changes in temperature, color, odor, and physical state.

4. When looking at a chemical equation, what key features do you see?
H2 + Cl2  2HCl

5. H2 + Cl2  2HCl Reactants Product
On the left side of the  you have the starting materials.
The starting materials are also known as the reactants
On the right side of the  you have the materials that are formed in the reaction.
The materials formed are also known as the products
H2 + Cl2  2HCl
Reactants
Product

6. H2 + Cl2  2HCl Chemical Equation
A statement using chemical formulas to describe the identities and relative amounts of the reactants and products involved in the chemical reaction.
This is an example of a chemical equation
H2 + Cl2  2HCl

7. Representing Chemical Reactions
Chemists use symbols to describe a chemical reaction.
Such symbols include:
+ separates two or more reactants or products
 separates reactants from products
(s) identifies a solid state
(l) identifies a liquid state
(g) identifies a gaseous state
(aq) identifies a water solution

8. Balancing Chemical Equations
Why is it important to have a balanced chemical equation?
Share your answer with your lab table.

9. Balancing Chemical Equations Cont.
Having a balanced equation insures that the law of conservation of mass is followed.
The law of conservation of mass states that mass is neither created nor destroyed during a chemical reaction.
In a chemical reaction we cannot create and destroy matter willy nilly, so we must have a balanced chemical equation to insure that, that doesn’t happen.

10. Balancing Chemical Equations Cont.
To balance a chemical equation you must have the correct coefficient for each chemical formula in your equation.
A coefficient is the number written in front of a reactant or product.
Coefficients are usually whole numbers
The number 1 is usually not written in the equation. If there is no coefficient then the 1 is assumed.

11. Is this correct??? Na(s) + Cl2(g)  NaCl(s) 2 Fe(s) + Cl2  FeCl3(s)
Work in your lab table groups.
Na(s) + Cl2(g)  NaCl(s)
2 Fe(s) + Cl2  FeCl3(s)

12. Steps for Balancing Chemical Equations
1. Write the skeleton equation for the reaction.
Tips:
Make sure that you have the correct formulas.
Remember the formula depends on the charges of the individual atoms.
The arrow separates the reactants from the products.

13. Steps for Balancing Chemical Equations
2. Count the atoms of the elements in the reactants.
Tips:
If a reaction involves identical polyatomic ions in the reactants and products, count the ions as if they are elements.

14. Steps for Balancing Chemical Equations
3. Count the atoms of the elements in the products.

15. Steps for Balancing Chemical Equations
4. Change the coefficients to make the number of atoms of each element equal on both sides of the equation.
Tips:
NEVER CHANGE THE SUBSCRIPT IN A CHEMICAL FORMULA TO BALANCE AN EQUATION.
This will change the identify of the substance

16. Steps for Balancing Chemical Equations
5. Write the coefficients in their lowest possible ratio.
Tips:
The coefficients should be the smallest possible whole number.

17. Steps for Balancing Chemical Equations
6. Check your work 
Make sure that the chemical formulas are written correctly.
Check to make sure that the number of atoms of each element is equal on both sides of the equation.

18. Sources
Textbook: Chemistry: Matter and Change. Copyright McGraw-Hill Companies, Inc.
Microsoft Clip Art