Understanding Chemical Reactions: Balancing Equations and Types of Reactions

1. Unit 7 Chemical Reactions Balancing Chemical Equations Types of Reactions

2. Chemical Reactions • Remember – A chemical change occurs when substances react together and form NEW products. • Examples of this include: • rusting • Combustion • Tarnishing • Fermentation • oxidation • Acid rain reacting with calcium in rocks

3. Indicators • Evolution of heat and light • Production of a gas • Formation of a precipitate • A precipitate is a solid produced as a result of a chemical reaction in solution and that separates from the solution • Unexpected Color change • Change in energy (absorption or evolution) • Formation of water • Production of an odor

4. Chemical reaction can be written in words or as formulas. When they are written using formulas and symbol this is called a chemical equation. • Chemical reactions must contain correct reactants (the beginning substances) and products (the ending substances)

5. Law of Conservation of Mass • Chemical equations must be BALANCED in order to follow the LAW of Conservation of Mass, which states that mass can neither be created or destroyed. • Remember… what you start with has to equal with what you end with!

6. To balance a chemical equation you must make sure there is the same number of each type of atom on both sides of the arrow. • Only change the coefficients (the number in front of the compounds or element), never change subscripts! • Diatomic molecules (di=2, atomic=atoms) • (always exist as 2 when they are by themselves) • N2 • O2 • F2 • Cl2 • Br2 • I2 • H2

7. Balancing Equations • Remember that when balancing an equation each side has to equal. (Law of Conservation of Mass). • First: • Write out the equation: ___N2 + ___H2 ___NH3 • Count how many atoms of each element are on each side. • Reactants Products • N=2 N=1 • H=2 H=3 • This equation is NOT balanced. • You will now have to add coefficients to make each side balanced.

8. ____N2 + ___H2  _____ NH3

9. Copy this table in your notes

10. The 5 major types of Chemical Reactions • Synthesis • 2 elements or simple compounds combine to form ONE product. • Examples: • Generic equation: A + X  AX • 8 Fe + S8  8 FeS • CaO + H2O Ca(OH)2

11. Decomposition • ONE compound is broken down into simpler parts • Examples: • Generic equations: • AX  A + X • AXY  AX +Y • 2 H2O  2 H2 + O2

12. Single Replacement • An element and a compound combine to form a new element and compound. • Metals can replace other metals and hydrogen in an acid. • Halogens can replace halogens. • Must look at activity series to determine if the reaction will occur (it is located on your reference sheet) • Generic equations: • AX + B  BX + A • AX + Y  AY + X • 2 Na + MgSO4  Mg + Na2SO4 • Cl2 + 2NaBr  Br2 + 2 NaCl

13. Double Replacement • 2 compounds produce 2 NEW compounds. • These compounds are in aqueous solution so the ions switch places with each other. • Must consider solubility rules to determine which product is the precipitate, if any. • Generic Equation: • AX + BY  AY + BX • Pb(NO3)2 + 2 KI  PbI2 + 2 KNO3

14. Combustion • Oxygen combines with a compound to produce carbon dioxide and water. • This releases large amounts of energy (heat). • Generic equation: • CxHy + O2 CO2 + H2O