THERMOCHEMICAL REACTIONS
Chemical reactions which emit or absorb heat energy is called thermochemical reactions.
Exothermic reactions
Chemical reactions which liberate heat are called exothermic reactions.
Example, add 5 mL dilute hydrochloric acid to a piece of magnesium taken in a test tube.
Observations:
As a result of reaction, Hydrogen gas liberated and the bottom of test tube got warm.
Magnesium + Hydrochloric acid o Magnesium chloride + Hydrogen + heat
Mg+2HCl—->MgCl2 +H2 +heat
Endothermic reactions
Chemical reactions which absorb heat are called endothermic reactions.
Example, take a few crystals of potassium permanganate in a dry test tube. Heat the test tube. Bring a glowing incense stick to the mouth of the test tube.
Observations:
Colour of potassium permanganate faded and the incense stick got lit.
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