BALANCING EQUATIONS REVIEW NOTES

Chapter 9

Law of Conservation of Matter• Chemical reactions occur when one or more

substances are rearranged to form new substances.

Ex: 2Na + H2O 2NaOH + H2

• Indicators of a chemical reaction:• Temperature change• Color change• Production of light• Production of gas (bubbles)• Formation of a solid (precipitate)

• Chemical equations are balanced using coefficients to satisfy the Law of Conservation of Matter• Coefficients = big numbers (can change)• Subscripts = small numbers (do NOT

change)

Ex: 2H2O

Parts of a Chemical Equation• Reactants are the starting substances in a

chemical reaction• The arrow points away from the reactants• Ex: 2H2 + O2 2H2O

• Products are the substances formed during a chemical reaction• The arrow points toward the products• Ex: 2H2 + O2 2H2O

• The state of matter can be found on the right side of a compound

(aq) = aqueous solution(s) = solid(l) = liquid(g) = gaseous

Steps to Balancing Equations1. Write formulas for all compounds (sometimes given) (remember your diatomic molecules)

2. Separate reactants and products by a line

3. Count how many atoms of each element are present on the reactant and the product side (element inventory)

4. Add or adjust the coefficients so that element inventory is balanced (subscripts cannot be changed)

5. Reduce coefficients to lowest possible terms (simplify)

6. Check your work

Types of Reactions• A chemical reaction that gives off energy is

exothermic• A chemical reaction that uses energy is

endothermic

Types of Reactions:1. Synthesis

A + B AB2. Decomposition

AB A + B3. Single Displacement (replacement) A + BX AX + B4. Double Displacement (replacement)

AX + BY BX + AY5. Combustion

C8H18 + O2 CO2 + H2O + ENERGY