TYPES OF REACTIONS

• One system which is convenient at an introductory level involves classifying reactions into four basic types.

• Knowing the different types of reaction allows the chemist to predict the products of the reactions of different substance.c

TYPES OF REACTIONS:

1.COMBINATION REACTION2.DECOMPOSITON REACTION3.SUBSTITUTION REACTION4.DOUBLE REPLACEMENT REACTION

1. COMBINATION REACTION

• Type of reaction in which two or more substances combine to form a more complex substance.

• Also called synthesis reaction • Form:

A + B -> AB

EXAMPLES:

• C ₍s₎ + O₂₍g₎ -> CO ₂₍g₎

• 2 Ca ₍s₎ + O ₂₍g₎ -> 2CaO ₍s₎

• N ₂₍g₎ + 3 H ₂₍g₎ -> 2NH ₃₍g₎

• 2 Na ₍s₎ + Cl ₂₍g₎ -> 2NaCl ₍s₎

2. DECOMPOSITION REACTION

Various conditions can cause a substance to decompose:• The most common type of a decomposition is

cause by a rise in temperature. This is called thermal decomposition.

Example:

2 HgO ₍s₎ ->(heat) 2Hg ₍g₎ + O ₂₍g₎

2KMnO ₄₍s₎ ->(heat) K ₂MnO ₄₍s₎ + MnO ₂₍g₎ + O ₂₍g₎

• If such a decomposition proceeds very fast, an explosion may occur

Example:

2NH₄NO ₃₍s₎ ->(heat) 4H₂O ₍g₎ + 2N ₂₍g₎ + O ₂₍g₎

• Light is another factor which may occur chemical decompositions to occur. Such decompositions are known as photo-chemical decompositions.

Example:

2AgBr ₍s₎ ->(light) 2Ag ₍s₎ + Br ₂₍g₎

• Although catalysts cannot cause chemicals to decompose, they can speed up the rate of a chemical decomposition. The addition of a tiny amount of manganese dioxide to a solution of hydrogen peroxide will immediately result in a vigorous evolution of oxygen gas.

Example:

2H ₂O ₂₍aq₎ ->(manganese dioxide/catalyst)2 H ₂O ₍l₎ + O ₂₍g₎

• Electricity can also be used to decompose compounds, resulting in electrolytic decomposition.

Examples:

2NaCl ->(electrolysis) 2Na + Cl ₂

PbBr ₂ ->(electrolysis) Pb + Br ₂

3. SUBSTITUTION REACTION• Also called single replacement reaction• Form:

C + AB -> CB + A• more active element replaces a less active element in

the compound.Example:

Fe + CuSO₄ -> FeSO₄ + Cu2 Na + 2H₂O -> 2NaOH + H₂

Metals:Lithium(Li) Chromium(Cr) Mercury(Hg)Potassium (K) Iron(Fe) Platinum(Pt)Barium(Ba) Cobalt(Co) Gold(Au)Calcium(Ca) Nickel(Ni)Sodium(Na) Tin(Sn)Magnesium(Mg) Lead(Pb)Aluminum(Al) Hydrogen(H₂)Manganese(Mn) Copper(Cu)Zinc(Zn) Silver(Ag)

Halogens:

Flourine(F)Chlorine(Cl)Bromine(Br)Iodine(I)

4. DOUBLE REPLACEMENT REACTION• Also called ionic reaction• Characterized by the exchange of ions

(charged atoms or molecules) between two compounds

• Form:

AB + CD -> AD + CB

Several types of double replacement reactions are frequently encountered:

1. A reaction between a base such as NaOH, KOH or Ca(OH)₂ in aqueous solution and an acid such as HCl, H₂SO₄ or CH₃COOH. Reactions of this type are called neutralizations and the products are always water molecules and salt.

HCl + NaOH -> NaCl + H₂O

H₂SO₄ + 2KOH -> K₂SO₄ + 2H₂O

2. A reaction between solutions of two soluble salts, a soluble salt and an acid, or a soluble salt and an alkali which, by exchanging cations and anions, can produce one insoluble compound.

Examples:

NaCl + AgNO₃ -> NaNO₃ + AgCl

BaCL₂ + MgSO₄ -> MgCl₂ + BaSO₄

Activity:

Given the type of reaction, predict the products and balance the equation.

1. Combination: Li + F₂2. Decomposition: CuCO₃3. Substitution: Mg + HCl4. Ionic reaction: AgNO₃ + BaCl₂

End …Thank you!