Question

Which of the following is not an endothermic reaction:
A.$\text{CaC}{{\text{O}}_{\text{3}}}\to \text{CaO + C}{{\text{O}}_{\text{2}}}$
B.$\text{2}{{\text{H}}_{\text{2}}}\text{O}\to \text{2}{{\text{H}}_{\text{2}}}\text{+}{{\text{O}}_{\text{2}}}$
C.\[\text{6C}{{\text{O}}_{\text{2}}}\text{+6}{{\text{H}}_{\text{2}}}\text{O}\to {{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}\text{+6}{{\text{O}}_{\text{2}}}\]
D.\[{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{12}}}{{\text{O}}_{\text{6}}}\text{+6}{{\text{O}}_{\text{2}}}\to \text{6C}{{\text{O}}_{\text{2}}}\text{+6}{{\text{H}}_{\text{2}}}\text{O}\]

Answer 1

Hint: An endothermic reaction can be defined as the one in which there is the energy that is accepted to carry out the reaction. Endothermic reactions occur between molecules which are generally non-reactive.

Complete step by step answer:
- The first reaction is the decomposition reaction of calcium carbonate and every decomposition reaction requires energy to proceed in the forward direction. Hence this reaction will be an endothermic reaction.
- The second reaction is the dissociation of water into its components hydrogen and oxygen. Both the formation as well as the dissociation of water requires energy as the reactant as well as the products are stable and requires energy for the bonds to be broken. Hence this is also endothermic.
- The third reaction is the reverse of the cellular oxidation reaction or it is the reaction for photosynthesis that takes place in the plant cells. Hence this process would require energy as is required during photosynthesis, the energy from the sunlight is taken. Hence this is also endothermic.
- The last one is the cellular oxidation reaction that takes place in the mitochondria of the cell and is saved in the form of ATP that provides us energy to carry out the day to day activities. Hence this reaction is exothermic in nature.

So, the correct answer is option D.

Note:
The exothermic reactions are the opposite of the endothermic reactions in which the energy is released after the reaction. This is due to the excess amount of bond formation energy that is released in comparison to the bond dissociation energy required.