Question

(a) What do you understand by exothermic and endothermic reactions ?

(b) Give one example of an exothermic reaction and one of an endothermic reaction.

(c) Which of the following are endothermic reactions and which are exothemic reactions ?

(i) Buring of natural gas (ii) Photosynthesis

(iii) Electrolysis of water (iv) Respitation

(v) Decomposition of calcium carbonate

Answer 1

(a)

Reactions in which heat is given out along with the products are called exothermic reactions.

Reactions that absorb energy or require energy in order to proceed are called endothermic reactions.

(b)

Exothermic reaction example: Burning of methane gas releases a large amount of energy.

CH₄ (g) + 2O₂ (g) → CO₂ (g) + 2H₂O (g)

Endothermic reaction example: When ammonium chloride is dissolved in water in a test tube, the test tube becomes cold. Thus the reaction is an example of endothermic reaction.

(c)
(i) Exothermic because , heat is released while burning Natural gas.
(ii) Photosynthesis; endothermic
(iii) Endothermic because, Electricity as heat is needed.
(iv) Respiration ; exothermic
(v) Endothermic because, Heat is needed to break down.