Question

Which of the following reactions is endothermic?

$$A.{\text{ }}CaC{O_3} \to CaO + C{O_2} \\\ B.{\text{ }}Fe + S \to FeS \\\ C.{\text{ }}NaOH + HCl \to NaCl + {H_2}O \\\ D.{\text{ }}C{H_4} + 2{O_2} \to C{O_2} + 2{H_2}O \\\$$

Answer 1

In order to solve the given problem first we will understand the difference between the endothermic and exothermic reaction further we will see what are the characteristics for a reaction to be classified as endothermic reaction along with some examples and typical reactions. Further on the basis of our characterization we will select the endothermic reaction amongst the given options.

Complete step by step answer:
First let us see the basic difference between the exothermic and endothermic reaction.
A chemical reaction in which the energy is stored in the form of heat is known as an endothermic reaction, whereas an exothermic reaction is known as a chemical reaction in which energy is emitted or evolves in the form of heat. The key distinction in these terms lies, however, in the type of energy that is used or emitted during every chemical reaction.
Simply stated, endothermic reactions consume energy in the form of heat from the atmosphere. An exothermic response, on the other hand, releases energy into the system's surroundings.
Whenever the energy used to split the bonds between the molecules is higher than the energy given out when bonds are formed in the products, an endothermic reaction takes place. This suggests that the reaction absorbs energy total, because there is a drop in temperature in the system.
Some practical example of endothermic reaction is:
Making ice cubes
Formation of snow in clouds
Condensation of rain from water vapor

On the basis of our understanding let us now find the endothermic reaction amongst the given options.
As we know that the dissociation reaction involves the breaking of a compound into two or more constituent particles in the compound and thus it will require external energy for its completion.
$CaC{O_3} \to CaO + C{O_2}$

As in option A, the reaction involves dissociation of calcium carbonate into calcium oxide and carbon dioxide, so the dissociation reaction of $CaC{O_3}$ requires external energy. Other than the first one every other reaction is exothermic in nature.
Hence, $CaC{O_3} \to CaO + C{O_2}$ is an endothermic reaction.

So, the correct answer is “Option A”.

Note: In order to solve such types of problems students must remember the basic difference between the endothermic and exothermic reaction which is also mentioned in the solution. The students must also remember some common and typical reactions and their types for an easy solution.