Page 83 - SCERT Kerala State Syllabus 8th Standard Basic Science Textbooks English Medium Part 1_Neat
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Thermo chemical reactions
Add 5 mL dilute hydrochloric acid to a piece of magnesium
taken in a test tube.
Which is the gas liberated in this reaction?
Touch the bottom of the test tube. What do you feel?
Why does the test tube get warm?
Heat was evolved along with formation of the products.
The balanced chemical equation of this reaction is as follows:
Magnesium + Hydrochloric acid Magnesium chloride +
Hydrogen + heat
Mg + 2HCl MgCl + H + heat
2 2
Flaring up a glowing incense stick
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. What do you observe?
The stick flares up. What could be the reason?
Does the residue in the test tube have the colour of
Fig. 6.4
potassium permanganate?
Can this reaction take place without heating? Try.
When potassium permanganate is heated, it decomposes to form
potassium manganate, manganese dioxide and oxygen.
Potassium permanganate + heat Potassium manganate
+ Manganese dioxide + Oxygen
In this reaction, potassium permanganate decomposes with
absorption of heat.
Add hydrochloric acid to a concentrated solution of sodium
hydroxide taken in a test tube. As the reaction proceeds, does
the test tube become hot or cold?
82 Basic Science VIII
