Tiêu đề 3. How things change & react with one another.pdf ✅

29. Zinc nitrate Zn (NO3)2 30. Ferrous oxide FeO 31. Ferric Oxide Fe2O3 32. Ferrous Chloride FeCl2 33. Ferric Chloride FeCl3 34. Ferrous sulphate FeSO4 35. Ferric Sulphate Fe2(SO4)3 36. Lead trioxide Pb3O4 37. Lead monoxide PbO 38. Mercury oxide HgO 39. Copper sulphate CuSO4  Chemical change In a chemical change, one or more new substances are created. The new substance is different from the original. It has properties that are different from those of the starting materials. In addition, you can get the original matter back conveniently. Consider an ordinary box of matches. A single match in a box can remain unchanged forever. However, if someone were to take the match and then light it a flame light up and the burns out. What remains will have changed forever. The match can never be lighted again. The match has undergone a chemical reaction. Chemical changes are irreversible changes. The following are the examples of chemical changes: a. Rusting of iron b. Burning of fuel such as, gas, petrol etc. c. Oxidising food for energy d. Lighting a match e. Decay of food, dead plant and animal bodies f. Cooking of food g. Butter turning sour h. Photosynthesis in plants i. Fermentation of fruit juice etc. j. Respiration in living being k. Digestion In the chemical change, gas is evolved; change of state, precipitate formation and the energy transfer takes place. Consider the following examples of chemical changes: a. Zinc reacts with hydrochloric acid to form Zinc chloride and hydrogen gas is evolved. Zn + 2HCl → ZnCl2 + H2 b. In the process of photosynthesis, solar energy is transferred or change to chemical energy CO2 + 12 H2O → C6H12O6 + 6H2O + 6O2 c. Two gaseous substance H2 and O2 react together to form wter, which is a liquid. This satisfies that the change of state takes place during a chemical change. 2H2(gas) + O2(gas) → 2H2O (liquid) d. Sindoor (vermillion) is chemically lead nitrate. When it is heated, the compound liberates oxygen and forms a yellowish substance called lead oxide. 2Pb3O4 → 6PbO + O2 ➢ RUSTING AND ITS PREVENTION Rusting is a significant difficulty because it wears off the structure of bridges, iron railings, machine parts, agricultural equipments such as khurpi, spade, sickle etc. Rusting is a type of corrosion. Eating away of metals due to oxygen, carbon dioxide, water vapour, hydrogen sulphide (a gas with pungent smell) etc. present in the atmosphere is called corrosion. Eating away of metals due to oxygen alone is called rusting. The powdery substance that is deposited on iron (metals) is called rust. Prevention of rusting has always been a challenge and involves a huge expenditure. Fe (iron) + O2 (Oxygen from atmosphere + H2O (from moisture water) = Fe2O3 (Ferric Oxide or rust) Rusting is a process of slow oxidation. It is a chemical change which is responsible for destroying the iron articles such a khurpi, kodal etc. slowly. By greasing and oiling of metal accessories, tools and machines.  The process of coating a metal with other suitable material to stop its contact with air, water or moisture is called galvanization. Iron sheets are dipped in molten zinc to coat the