TYPES OF CHEMICAL REACTIONS
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1. Combination Reaction
2. Decomposition Reaction
3. Displacement Reaction
4. Double Displacement Reaction
5. Oxidation and Reduction Reaction
A. COMBINATION REACTION
Those reactions in which two or more substances combine to form a single substance, are called combination reaction.
Examples:
1. Burning of Magnesium in air.
2. Formation of water from hydrogen and oxygen.
3. Burning of carbon to form carbon dioxide.
4. Reaction between hydrogen and chlorine to form hydrochloric acid.
5. Sodium metal burns in chlorine to form sodium chloride.
6. When iron powder is heated with sulphur, iron sulphide is formed.
7. Calcium oxide reacts vigorously with water to form calcium hydroxide.
8. Ammonia reacts with hydrogen chloride to form ammonium chloride.
9. Carbon monoxide reacts with oxygen to form carbon dioxide.
10. Sulphur dioxide reacts with oxygen to produce sulphur trioxide.
B. DECOMPOSITION REACTIONS
Those reactions in which a compound splits up into two or more simpler substances are known as decompostion reactions. It always needs energy either in form of heat, light or electricity to carry out a decompostion reaction.
When a decompostion reaction is carried out by heating, it is called "thermal decomposition".
Examples.
1. When calcium carbonate (CaCO₃) is heated, it decomposes to give calcium oxide (CaO) and carbon dioxide (CO₂). (Thermal decomposition)
2. When Potassium chlorate (KClO₃)
is heated in the presence of manganese dioxide catalyst, it decomposes to give potassium chloride (KCl) and oxygen (O₂). (Thermal decomposition)
3. When ferrous sulphate (green) (FeSO₄) is heated strongly, it decomposes to form ferric oxide (brown) (Fe₂O₃), sulphur dioxide (SO₂) and sulphur trioxide (SO₃). (Thermal decomposition)
4. When colourless lead nitrate Pb(NO₃)₂ is heated strongly, it breaks down to form simpler substances like yellow lead monoxide PbO, Nitrogen dioxide NO₂ and oxygen O₂. (Thermal decomposition)
5. When electric current is passed through acidified water, it decomposes to give hydrogen gas and oxygen gas. (Decomposition using electricity)
6. When electric current is passed through molten sodium chloride, it decomposes to give sodium metal and chlorine gas. (Decomposition using electricity)
7. When electric current is passed through molten aluminium oxide Al₂O₃, it decomposes to give aluminium metal and oxygen gas. (Decomposition using electricity)
8. When Silver Chloride is exposed to light, it decomposes to form silver metal and chlorine gas. (Decomposition using light energy)
9. When silver bromide (pale yellow) (AgBr) is exposed to light, it decomposes into silver metal (greyish white) and Bromine gas. (Decomposition using light energy).
Uses of Decomposition Reactions
The decomposition reactions using electricity are used to extract several metals like Aluminium, Sodium from their chlorides or oxides.
Like when fused or molten metal chlorides or oxides is decomposed by passing electricity, metals are produced in the Cathode (negative electrode).
Decomposition Reactions in our body
The digestion of food in our body is an example of decomposition reaction. Like complex carbohydrates (starch) decomposes into simple sugar and proteins into amino acids.
DISPLACEMENT REACTIONS
Those reactions in which one element takes place of another element in a compound, are known as displacement reactions.
A more reactive elements always displaces a less reactive element from its compound.
Metal Reactivity Series
(How to remember reactivity series)
1. Please. Potassium
2. Stop. Sodium
3. Calling. Calcium
4. Me. Magnesium
5. A. Aluminium
6. Careless. Carbon
7. Zebra. Zinc
8. Instead. Iron
9. Try. Tin
10. Learning. Lead
11. How. Hydrogen
12. Cow Copper
13. Saves. Silver
14. Goat. Gold
1. As Zinc is more reactive than Copper, When a strip of Zinc metal is placed in Copper sulphate solution, then Zinc displaces Copper and Zinc Sulphate solution and Copper are obtained.
CuSO₄ (aq) (blue solution) + Zn (s) (silvery white) → ZnSO₄ (aq) (colourless solution) + Cu (s) (red brown)
2. When a piece of Magnesium metal is placed in copper sulphate solution and Copper metal are formed.
CuSO₄ (aq) (blue solution) + Mg (s) → MgSO₄ (aq) (colourless solution) + Cu (s) (red brown)
As Magnesium is more reactive than Copper.
3. When a piece of Iron metal is placed in Copper Sulphate solution, then Iron (II) Sulphate solution and Copper metal are formed.
CuSO₄ (aq) (blue solution) + Fe (s) → FeSO₄ (aq) (greenish solution) + Cu (s) (red brown)
As Iron is more reactive than Copper.
4. When a strip of lead metal is placed in a solution of copper chloride, then lead chloride solution and copper metal are formed.
CuCl₂ (aq) (green solution) + Pb (s) → PbCl₂ (aq) (Lead Chloride) (colourless solution) + Cu (s) (red brown)
As Lead (Pb) is more reactive than Copper (Cu)
5. When a copper strip is placed in a solution of silver nitrate, then copper nitrate solution and silver metal are formed.
2AgNO₃ (aq) (colourless solution) + Cu (s) (red brown) → Cu(NO₃)₂ (aq) (blue solution) + 2Ag (s) (Greyish white)
As Copper (Cu) is more reactive than Silver (Ag)
6. Iron metal reacts with dilute hydrochloric acid to form iron(II) chloride and hydrogen gas.
Fe (s) + 2HCl (aq) → FeCl₂ (aq) + H₂ (g)
As Iron is more reactive than Hydrogen.
7. Magnesium metal reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen gas.
Mg (s) + 2HCl (aq) → MgCl₂ (aq) + H₂ (g)
As Magnesium is more reactive than Hydrogen.
8. Sodium metal reacts with water to form sodium hydroxide solution and hydrogen gas.
2Na (s) + 2H₂O (l) → 2NaOH (aq) + H₂ (g)
As Sodium is more reactive than Hydrogen.
9. Chlorine gas reacts with potassium iodide solution to form potassium chloride and iodine.
Cl₂ (g) + 2KI (aq) → 2KCl (aq) + I₂ (s)
Chlorine displaces iodine from potassium iodide.
10. When copper oxide is heated with magnesium powder, then magnesium oxide and copper are formed.
CuO (s) + Mg (s) → MgO (s) + Cu (s)
Magnesium displaces Copper from from its oxide.
12. When iron (III) oxide is heated with Aluminium powder, then aluminium oxide and iron metal is formed. The excessive heat produced during the reaction makes the iron to be melted.
Fe₂O₃ (s) + 2Al (s) → Al₂O₃ (s) + 2Fe (l) (molten iron)
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