Predict whether the following reactions will be exothermic or endothermic. Reaction A. N 2 ( g ) + 3 H 2 ( g ) ⟶ 2 NH 3 ( g ) Reaction B. S ( g ) + O 2 ( g ) ⟶ SO 2 ( g ) Reaction C. 2 H 2 O ( g ) ⟶ 2 H 2 ( g ) + O 2 ( g ) Reaction D. 2 F ( g ) ⟶ F 2 ( g )

Answer :

Exothermic reactions : A, B, D

Endothermic reaction : C

Explanation :

Endothermic reaction : It is defined as the chemical reaction in which the energy is absorbed from the surrounding.

In the endothermic reaction, the energy of reactant are less than the energy of product.

Exothermic reaction : It is defined as the chemical reaction in which the energy is released into the surrounding.

In the exothermic reaction, the energy of reactant are more than the energy of product.

As we know that, heat is released in the bond formation and heat is required in the bond breaking.

Reaction (A):

In this reaction, the more bonds are formed than the bond broken. That means, heat will be released. So, It is an exothermic reaction.

Reaction (B):

In this reaction, burning of sulfur with oxygen takes place. That means, heat will be released. So, It is an exothermic reaction.

Reaction (C):

This reaction is a decomposition reaction. That means, heat will be required. So, It is an endothermic reaction.

Reaction (D):

In this reaction, formation of fluorine molecule from its atoms releases heat. So, It is an exothermic reaction.

Hence, the exothermic reactions are, A, B, D and endothermic reaction is, C