1. Balancing Equations

2. What is a chemical equation?
A chemical equation is shorthand way of expressing a chemical reaction.
A chemical equation describes what happens in a chemical reaction. One or more chemical changes that occur at the same time are called chemical reactions.
A chemical equation can be written in words or symbols. The symbolic equation identifies:
the reactants (starting materials)
the products (resulting substance)
the formulas of the participants and the amount of each substance.
Balancing a chemical equation refers to establishing the mathematical relationship between the quantity of reactants and products.

3. What is the Law of Conservation of Matter?
Law of Conservation of Matter states that matter cannot be created nor destroyed.
Therefore, it also states that mass is always conserved in a chemical reaction; the total mass of the products is always equal to the total mass of the reactants in a chemical reaction.

4. What does this have to do with chemical equations?
It means that the number of atoms of an element must be equal on both sides of an equation. In other words, the equation must be balanced.

5. Important Terms
Co-efficients are integers placed in front of the formula or a chemical symbol for an element.
State of matter: letters indicate the compound’s state: (g) for gas; (l) for liquid; (s) for solid; (aq) for aqueous (dissolved in water)

6. **Important**
In balancing equations, you CANNOT CHANGE SUBSCRIPTS! If you change a subscript, you change the substance. That would mean you are no longer balancing the same chemical REACTION anymore.

7. How do you make the numbers work out if you can’t change them?
You add numbers called COEFFICIENTS. Sound familiar? Heard that term in math before? You are right! A coefficient is added in front of a compound ONLY, and it distributes to all the elements in the compound.
It takes practice to be able to write balanced equations. There are essentially three steps to the process:

8. 1. Write the unbalanced equation.
• Chemical formulas of reactants are listed on the left hand side of the equation.
• Products are listed on the right hand side of the equation.
Reactants and products are separated by putting an arrow between them to show the direction of the reaction.

9. Example Problem
Tin oxide is heated with hydrogen gas to form tin metal and water vapor.
Write the balanced equation that describes this reaction:
SnO2 + H2 → Sn + H2O

10. SnO2 + H2 → Sn + H2O
This equation as it is is called a skeleton equation: it simply shows the formulas of the reactants and the products.
Refer to Table of Common Polyatomic Ions and Formulas of Ionic Compounds if you have trouble writing the chemical formulas of the products and reactants.

11. SnO2 + H2 → Sn + H2O Balance the equation.
Apply the Law of Conservation of Mass to get the same number of atoms of every element on each side of the equation. Tip: Start by balancing an element that appears in only one reactant and product.
Once one element is balanced, proceed to balance another, and another, until all elements are balanced.
Balance chemical formulas by placing coefficients in front of them. Do not add subscripts, because this will change the formulas.

12. SnO2 + H2 → Sn + H2O
Look at the equation and see which elements are not balanced. In this case, there are two oxygen atoms on the lefthand side of the equation and only one on the righthand side. Correct this by putting a coefficient of 2 in front of water:
SnO2 + H2 → Sn + 2 H2O

13. This puts the hydrogen atoms out of balance
This puts the hydrogen atoms out of balance. Now there are two hydrogen atoms on the left and four hydrogen atoms on the right.
To get four hydrogen atoms on the right, add a coefficient of 2 for the hydrogen gas. Remember, coefficients are multipliers, so if we write 2 H2O it denotes 2x2=4 hydrogen atoms and 2x1=2 oxygen atoms.
SnO2 + 2 H2 → Sn + 2 H2O
The equation is now balanced. Be sure to double-check your math! Each side of the equation has 1 atom of Sn, 2 atoms of O, and 4 atoms of H.

14. Counting Atoms to Balance Equations:
This is based on the Law of Conservation of Mass
Consider the following equation:
CH4 + 2O2  2H2O + CO2
Reactants: C = 1, H = 4, 0 = 4
Products: C = 1, H = 4, O = 4

15. Let’s try one! Al + O2  Al203 Step 1: Is it balanced? Al=1 Al=2
O= O=3
NO!
What are you going to do?

16. Did you get the answer?
4Al + 3O2  2Al2O3

17. Hints for Writing Word Equations:
Use the chemical symbol of the element when they are not in a compound (example Copper = Cu)
Three common compounds containing hydrogen that you MUST memorize: methane (CH4) ammonia (NH3) water (H2O)
Seven diatomic elements – when they do not occur on their own (not in a compound) they are always paired:
H2, N2, O2, F2, Cl2, Br2, I2, (all –gens, special seven)

18. Strategies for Balancing Equations:
Use trial and error (work in pencil)
Balance compounds first and single elements last
Finish balancing all atoms in one formula after you have placed a coefficient in front
NEVER CHANGE SUBSCRIPTS
Balance hydrogen and oxygen last as they often are in more than one reactant or product
ALWAYS double check that your reactants and products are equal.