Question

A reaction in which heat is absorbed is called an endothermic reaction. If true enter 1 else 0.

Answer 1

Hint: Endothermic word is made up of ‘endo’ which means ‘within’ and ‘thermal’ which means ‘heat energy’. Also this type of reaction increases the energy of the system.

Complete answer:
-Those reactions in which the reaction absorbs heat energy (thermal energy) from its surroundings and forms products are known as endothermic reactions. When these reactions absorb heat from outside sources they lower the temperature of the surroundings and thus cause a cooling effect. We can also say that such reactions increase the enthalpy or internal energy of the system.
-These reactions involve the formation of new chemical bonds by the absorption of thermal energy from the environment.
The opposite of endothermic is exothermic when bonds break and generate thermal energy.
-Considering a reaction for understanding purpose:
                                                        $A + B + q \to C + D$
Here q refers to the thermal or heat energy absorbed during the reaction. The enthalpy of the reaction can be written as: $\Delta {H_{rxn}} = {H_P} - {H_R} = + q$
Where, ${H_P}$ = enthalpy of products
                ${H_R}$= enthalpy of reactants
So, for endothermic reactions: $\Delta {H_{rxn}} = + ve$ and it indicates that heat is absorbed during such reactions.
Hence: ${H_R} + q = {H_P}$
-Also this reaction causes decrease in the entropy of the surroundings ($\Delta S < 0$).
-Examples of endothermic reactions are:
  (A) Ice cubes melt into liquid by absorbing heat energy from the surroundings.
  (B) When dissolved in water, ammonium chloride ($N{H_4}Cl$) absorbs energy and dissociates into ammonium ($N{H_4}^ + $) and chloride ($C{l^ - }$) ions. This can be represented in reaction form:
                      $N{H_4}Cl(s) + {H_2}O(l) + heat \to NH_4^ + (aq) + C{l^ - }(aq)$
  (C) Formation of nitric oxide (NO) by reacting nitrogen with oxygen is also an endothermic reaction.
  (D) Sublimation of solid $C{O_2}$.
  (E) Evaporation of liquid water to form water vapour.

Since this statement is true, we will enter: 1.

Note:
Absorption of energy causes a favourable increase in the entropy of the system ($\Delta S > 0$) so that the system overcomes the increase in enthalpy and its Gibbs energy still remains negative (process can be spontaneous). So, for endothermic reactions to be spontaneous another driving force besides enthalpy is entropy.