Question

What is meant by exothermic and endothermic reactions? Give examples?

Answer 1

Hint : A chemical reaction describes the formation of new species i.e. products from the starting substrates i.e. reactants by involving the making and breaking of bonds. On the basis of energy exchange, chemical reactions are classified into two categories. 1) Exothermic reactions and 2) Endothermic reactions.

Complete Step By Step Answer:
On the basis of energy exchange, chemical reactions are classified into two categories i.e. exothermic reactions and endothermic reactions. Exothermic reactions are those in which energy is released from the system to the surrounding. This energy is released in the form of heat, sound and light. For these reactions, the heat of the reaction ( $\Delta H$ ) has a negative value and the temperature of the system increases. The formation of common salt i.e. $NaCl$ from sodium ion $(N{{a}^{+}})$ and chloride ion $(C{{l}^{-}})$ is an example of exothermic reaction. In contrast, endothermic reactions are those in which energy is absorbed from the surrounding to the system. Photosynthesis is the endothermic process in which energy is absorbed from the sunlight by plants and thus converts carbon dioxide $(C{{O}_{2}})$ and water $({{H}_{2}}O)$ into glucose $({{C}_{6}}{{H}_{12}}{{O}_{6}})$ and oxygen $({{O}_{2}})$ . For this reaction, the heat of the reaction ( $\Delta H$ ) has a positive value and the temperature of the system decreases.

Note :
It is important to note that exothermic reactions are those in which energy is released in the form of heat and light. On the other hand, endothermic reactions are those in which energy is absorbed. The formation of common salt is an example of exothermic reaction while photosynthesis is an endothermic process.