Types of Chemical Reactions

Question 1

Combination Reaction

Answer 1

Two or more reactants combine to form a single product.
Eg. Mg + O2 = MgO + energy
C + O2 = CO2
H2 + O2 = H20
H2 + Cl2 = Hcl

Question 2

Decomposition Reaction

Answer 2

A single reactant splits up into two or more simpler products.
CaCO3 -> [heat] CaO + CO2
H20 -> [electricity] H2 + O2
CuSO4 . 5H20 -> [heat] CuSO4 + 5H20 (dull white)
AgCl (volatile) -> [sunlight] Ag + Cl2 (grey)

Question 3

Differentiate between physical and chemical changes.

Answer 3

PHYSICAL CHANGES
1. reversible
2. no change in chemical composition
3. compounds can be separated using physical changes
4. no new substance is formed

CHEMICAL CHANGES
1. irreversible
2. change in chemical composition
3. compounds are separated using chemical methods
4. new substance is formed

Question 4

List and explain the three types of decomposition reactions.

Answer 4

Thermolysis - decomposition by heat
FeSO4 . 7H2O (green) -> [mild heat] FeSO4 + 7H2O (white)
FeSO4 -> [strong heat] Fe2)3 (reddish-brown solid) + SO2SO3

Electrolysis - decomposition by electricity
H2O -> [electricity] H2 + O2

Photolysis - decomposition by light
AgCl (white) -> [sunlight] Ag (grey) + Cl2 {gas}

Question 5

Displacement Reaction

Answer 5

Takes place when a more reactive metal displaces a less reactive metal in a solution
Eg. Fe + CuSO4 -> FeSO4 + Cu(s)
Zn + HCl -> ZnCl2 + H2
{hydrogen gas gets displaced}

Question 6

Double Displacement Reaction

Answer 6

Mutual exchange of ions takes place between reactants.
BaCl2 + Na2SO4 -> BaSO4 + NaCl (precipitate) (insoluble salt)
NaOH + HCl -> NaCl + H2O
Pb(NO3)2 (lead nitrali) + KI (potassium iodine) -> PbI2 (lead iodine) + KNO3

Question 7

Define reactivity series of metals.

Answer 7

An order in which metals are arranged in decreasing order of their reactivity.

Question 8

Reactivity Series of Metals

Answer 8

Potassium
Sodium
Barium
Calcium
Magnesium
Aluminium
Zinc
Iron
Lead
Nickel
Hydrogen
Copper
Mercury
Silver
Gold
Platinum