Chemical prop.

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  • Characteristics of chemical reactions
    • Evolution of gas
      • When Zinc granules react with hydrochloric acid  it results in the formation of hydrogen gas in the form of bubbles can be observed and confirmed with the pop sound
        • Zn + 2HCl à ZnCl2 + H2 
    • Change in state
      • When wax is burnt in the form of candle it forms water and carbon di oxide and the solid wax changes into liquid and gas
    • Formation of precipitate
      • Barium chloride reacts with sodium sulphate to form Barium sulphate and sodium chloride
        • 2KI(aq) + Pb(NO3)2(aq) -> 2KNO3(aq) + PbI(s)
    • Change in colour
      • potassium    per manganate + lime juice leads to fading of purple colour and eventually loss of purple colour
    • Change in temperature
      • Endothermic
        • Absorption of heat           Eg: When barium hydroxide and ammonium chloride react to form barium chloride a lot of heat is absorbed and there is a decrease in temperature
          • Ba(OH)2 * 8H2O (s) + 2 NH4Cl (s) --> BaCl2 * 2H2O (s) + 2 NH3 (aq) + 8H2O (l)
      • Exothermic
        • Loss of heat Eg: Quick lime reacts with water to form calcium hydroxide with a lot of evolution of heat and there is a rise in temperature


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