CHEMICAL REACTIONS
FOR 1 TO 1 ONLINE CLASSES OVER ZOOM PLATFORM AT REASOBLE PRICE
BOOK YOUR CLASS, CALL AT 7002561074
Chemical reactions are the processes in which new substances with new properties are formed. During a chemical reaction, atoms of one element do not change into those of another element. Only a rearrangement of atoms takes place in a chemical reaction.
Example:
(i) When hydrogen combines with oxygen water is produced, which is different from hydrogen as well as oxygen, it is an example of chemical reaction.
(ii) The burning of magnesium in air to form magnesium oxide is an example of chemical reaction.
(iii) Souring of milk, Formation of curd from milk, Cooking of food, Digestion of food in our body, Process of respiration, Fermentation of grapes, Rusting of iron, Burning of fuels, Burning of candle wax, and Ripening of fruits are examples of chemical reactions.
REACTANTS
The substances which take part in a chemical reaction are called reactants.
PRODUCTS
The new substances produced as a result of chemical reaction are called products.
CHARACTERISTICS OF CHEMICAL REACTION
1. Evolution of a gas
When one of the products is a gas.
Examples:
a. When zinc granules (Zn) reacts with dilute sulphuric acid (H₂SO₄) then zinc sulphate (ZnSO₄) and hydrogen gas (H₂) is produced. Here, hydrogen gas is evolved.
b. When sodium carbonate Na₂CO₃ reacts with dilute hydrochloric acid HCl it produces carbon dioxide CO₂ gas. It is also an example of evolution of gas.
2. Formation of a precipitate
When one of the products is insoluble in water.
a. When carbon-di-oxide CO₂ is passed through lime water CaO, Calcium Carbonate CaCO₃ is precipitated.
b. When Potassium Iodide (KI) reacts with lead nitrate PbNO₃ then Potassium nitrate KNO₃ is formed which is insoluble in water hence precipitated.
c. When Barium Chloride BaCl₂ reacts with sulphuric acid (H₂SO₄), white Barium Sulphate BaSO₄ is produced, which is insoluble in water and hence precipitated.
3. Change in colour
When the products have different colours than that of the reactants.
a. When citric acid mixed with purple coloured Potassium Permanganate, the solutions turned to be colourless.
b. When sulphur di oxide gas reacts with acidified orange coloured potassium dichromate, the solution turned to be green.
4. Change in temperature
Some chemical reactions are characterized by a change in temperature. For example, when quicklime (CaO) reacts with water, then slaked lime Ca(OH)₂ is formed and a lot of heat energy is produced. Therefore, it is a chemical reaction which produces change in temperature.
Exothermic Chemical Reaction
The chemical reaction which produces heat when reaction occurs is called an exothermic chemical reaction. The temperature always increases during an exothermic chemical reactions.
Example: (i). CaO + H₂O → Ca(OH)₂
Quicklime reacts with water to produce slaked lime and heat
(ii). Zn + H₂SO₄ → ZnSO₄ + H₂
Zinc granules reacts with dilute sulphuric acid to produce zinc sulphate and hydrogen and heat.
Endothermic Chemical Reaction
The chemical reactions which absorb heat during the reaction are called endothermic chemical reactions.
Example:
(i). N₂ + 3H₂ → 2NH₃
Nitrogen reacts with hydrogen to produce ammonia by absorbing heat from surrounding.
(ii). Ba(OH)₂ + NH₄Cl → BaCl₂ + NH₃ + H₂O
Barium hydroxide reacts with ammonium chloride to produce Barium chloride ammonia and water by absorbing heat from surrounding.
5. Change in state
Some chemical reactions are characterized by a change in state.
Example: When wax is burned, then water and carbon dioxide are formed. Thus, the combustion of wax is characterized by a change in state from solid to liquid and gas.
No comments:
Post a Comment