Chemical Reactions

Why do reactions occur?

• The key is bond formation/ fulfilling the octet requirement for each element.

Reaction Basics

• Reactants react to yield Products

• Reactants → Products

• A + B → C + D

Symbols to know

yields reversible reaction

• + and

• (s) solid

• (l) liquid

• (g) gas

• (aq) aqueous

More Symbols

• ↓ precipitate is formed

• ↑ a gas is produced over the yields means heat added

(endothermic)

• + energy after the products means heat lost (exothermic)

Types of Reactions

• Synthesis (Combination)

• Decomposition (Analysis)

• Displacement (Single Replacement)

• Metathesis (Double Displacement)

• Combustion

Synthesis

• 2 or more elements combine to form a single compound

• Example: formation of Iron (III) oxide

Decomposition

• One compound separates into 2 or more substances

• Example: Electrolysis of water

Displacement

• A free element replaces another element in a chemical bond

• 2 Types– Cationic: metal replaces a metal in a bond– Anionic: non-metal replaces a non-metal in a

bond

Metathesis

• The exchange of ions between two compounds

• Usually forms precipitates

Combustion

• A special type of synthesis involving the addition of oxygen

• May or may not be “explosive”

Balancing Equations

BALANCE: N2 + H2 NH3

N2 + H2 NH32 3

K + H20 KOH + H2222

Both sides of the yields must be equal in atoms!

Hints

• Save Hydrogen and Oxygen for the last ones to balance

• Be on the look-out for polyatomic ions on each side (you can treat them as an element for balancing)

• Be aware of the diatomic elements!

Diatomic Elements

• Found naturally existing as pairs of atoms

• Prefer to be as a pair rather than alone

• H, N, O, F, Cl, Br, I, At

• Ex. Hydrogen reacts with sulfur to yield hydrogen sulfide

Try these:

• Fe + S Fe2S3

• H2O H2 + O2

• Al + H2SO4 Al2(SO4)3 + H2

Reaction Type Lab

• You will perform each of the types of reactions that we have studied. You will then write balanced chemical equations for each of the reactions and identify which type of reaction has occurred. Be sure to make notes and observations to support your idea of chemical change.

Reaction Type Lab

Reaction # Observations Balanced equation

Reaction Type

1

2

3

4