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CHEMICAL CHANGES, , Chemical changes and physical changes., , If a new substance (molecules) is formed in a change, it is called chemical change., Example: Burning of magnesium ribbon, burning of paper, reaction between acid and metal., But in a physical change, only a change in the arrangement of molecules are occurs. Physical change is a, temporary change., , Example: Melting of ice, vapourisation of water., , Thermochemical reaction., , Chemical reaction which liberates or absorbs heat energy is called thermochemical reaction., , If heat is liberated it is known as exothermic reaction., , Example: Burning of fire wood, reaction between acid and metal., , The reaction which absorbs heat energy is called endothermic reaction., , Example: The decomposition of potassium permanganate., , Potassium permanganate + heat — Potassium manganate + manganese dioxide + oxygen., , Photo chemical reaction., , The reaction which absorbs or releases light is called photo chemical reaction., , Example.1. Photo synthesis., , Water + Carbon dioxide + light - Glucose + Oxygen. (6H2O + 6CO: + light + CsHi20¢ +602), , It is our experience that most of the medicines are stored in brown bottles. It is for preventing light from, entering into the bottle that contain photosensitive medicine. 4] 1 ~., Electrolysis | |!, The process of decomposition of a substance by absorbing electric energy is | r, known as Electrolysis. :, The arrangement of the electrolysis of copper sulphate solution is given here., , Two carbon rods A & C are dipped in copper sulphate solution. When current is, , passed through the solution, copper deposits on the carbon rod C which is, connected to the negative of the battery and disappears the blue colour of the, , 4, , , , liquid., , Electrochemical cell., , The arrangement where electricity is produced due to chemical reaction LED, , is called Electrochemical cell. The figure of an electrochemical cell is 6 2 Switch, , , , shown., Here the current is produced due to the reaction of metal immersed in the, acid., , , , , , , , ‘Copper, Zine, , Dilute, sulphuric, acid, , , , Electrochemical Reaction., , A reaction where electricity is generated or absorbed is called, electrochemical reaction., , Electrolysis and Electrochemical cells are, , examples for electrochemical reaction., , For making an Electrochemical cell, we need an +, , acid. Since lemon,vegetables and most of the, , fruits contain acids, electrochemical cells can be;, , made using any of these. An electrochemical, , cell using lemon, copper and zinc is shown here.