Section 2 - Types of Reactions

• Classify 5 major types.• Predict the products• For some, we will be able to predict whether

or not they will happen at all.

How to recognize which type• Look at the reactants:

A + B AB Combination (Synthesis)

AB A + B Decomposition

AX + B A + BX Single Replacement

AX + BY AY + BX Double replacement

CxHy + O2 CO2 + H2O Combustion

Combination (Synthesis)

• A + B AB

• H2 + O2 H2O

• Ca +O2 ® CaO

• SO3 + H2O ® H2SO4

• We can predict the products if the reactants are two elements.

• Mg + N2 ® ____

Decomposition• To break apart

• AB A + B• H2O H2 + O2

• one reactant breaks apart into two or more elements or compounds.

• NaCl Na + Cl2 • CaCO3 CaO + CO2

• Note that energy (heat, sunlight, electricity, etc.) is usually required

Combination

Mg + O2 ®

Na + Cl2 ®

Decomposition

H2O ®

HgO ®

Single-Replacement Reaction• A + BX AX + B• One element replaces another

• Reactants must be an element and a compound.

• Products will be a different element and a different compound.

• Na + KCl ® K + NaCl• F2 + LiCl ® LiF + Cl2

Single-Replacement Reaction

• Only more reactive metals can replace a metal already in solution.

• The activity series (p. 333) lists the relative reactivity of metals.

• Higher on the list replaces lower metals.

The Activity Series of the Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold

1) Metals can replace other metals provided that they are above the metal that they are trying to replace.• The single metal is above

the metal in the compound• If it isn’t, there is no reaction

2) Metals above hydrogen can replace hydrogen in acids.

3) Metals from lead upward can replace hydrogen in water.

Higher activity

Lower activity

Double-Replacement Reaction• Two things replace each other.• AX + BY AY + BX

• NaOH + FeCl3 ® Fe(OH)3 + NaCl– Reactants must be two ionic compounds.– Usually in aqueous solution

Double Replacement• Has certain “driving forces”

–Will only happen if one of the products:

a) doesn’t dissolve in water and forms a solid (a “precipitate”), or

b) is a gas that bubbles out, or

c) is a molecular compound (usually water).

• CaCl2 + NaOH

• KOH + Fe(NO3)3

Complete and Balance

• CaCl2 + NaOH

• KOH + Fe(NO3)3

Single-Replacement

Zn + H2SO4 ®

KBr +Cl2 ®

Double Replacement

AgNO3 + NaCl ®

Mg(OH)2 + H2SO3 ®

Combustion Reaction• Means “add oxygen”• CxHy + O2 CO2 + H2O

• Normally, a compound composed of only C, H, (and maybe O) is reacted with oxygen – usually called “burning”

• If the combustion is complete, the products will be CO2 and H2O.

• If the combustion is incomplete, the products will be CO (or possibly just C) and H2O.

Combustion Reaction Examples

• C4H10 + O2 ® H2O + CO2

• C4H10 + O2 ® H2O + CO

• C6H12O6 + O2 ® (complete)

• C8H8 +O2 ® (incomplete)

Combustion (complete)

C6H12O6 + O2

C3H8 + O2