Question

A chemical reaction in which heat is evolved is called a/ an:
A.Exothermic reaction
B.Endothermic reaction
C.Thermite reaction
D.Catalytic reaction

Answer 1

Hint: The process of chemical transformation of one set of a chemical substance into another set is termed as a ‘chemical reaction’.
An exothermic reaction leads to an increase in the temperature of the surroundings while an endothermic reaction leads to a decrease in the temperature of the surroundings.

Complete step by step answer:
-It is known that energy is conserved in chemical reactions which mean that the total amount of energy at the end of a reaction is the same as the total amount of energy at the beginning of the reaction.
-During a chemical reaction, energy is transferred to or from the surroundings.
If during a chemical reaction, energy or heat is transferred to the surroundings or in other words, heat is evolved is called an exothermic reaction. Thus, the temperature of the surroundings increases. Combustion reactions, oxidation reactions and neutralization reactions are exothermic reactions.
-For example, the neutralization reaction between sodium hydroxide and hydrochloric acid is an exothermic reaction because when sodium hydroxide is poured in a beaker having hydrochloric acid and a thermometer, the thermometer shows a rise in temperature. So, option A is correct.
-If during a chemical reaction, energy or heat is taken in from the surroundings or in other words, heat is absorbed is called an endothermic reaction. Thus, the temperature of the surroundings decreases. Thermal decomposition reactions are endothermic reactions.
For example, the reaction between sodium carbonate and ethanoic acid is an endothermic reaction because the thermometer shows a fall in temperature. So, option B is wrong.
-A thermite reaction is a type of reaction in which aluminium metal is oxidized by an oxide of another metal. So, option C is wrong.
-Catalytic reactions are reactions in which catalysts are used to increase the rate of the reaction without itself being consumed. So, option D is wrong.

Hence option A is correct.

Note:
-In an exothermic reaction, energy is released in the form of heat, light, electricity or sound but in an endothermic reaction, energy is in the form of heat only.
-Exothermic reactions which are uncontrollable, such as those leading to fire and explosions are wasteful as it is very difficult to capture the released energy.