Question

Based on relative bond strengths, classify these reactions as endothermic (energy absorbed) or exothermic (energy released ).

Answer 1

Concepts and reason

The concept of exothermic or endothermic reaction is used in the problem. On the basis of comparison between the stability of reactions and products, a reaction is said to be exothermic or endothermic.

Fundamentals

A reaction is exothermic or endothermic on the basis of the feasibility of the reaction. If products are more stable than reactants, reaction is exothermic and if reactants are more stable than products, reaction is endothermic.

Also, stronger are the bonds, more stable is the molecule.

In the reaction

${{\rm{A}}_2} + {{\rm{C}}_2}\longrightarrow{{}}2{\rm{AC}}$

As A-C bond is weaker than A-A and C-C, this is an endothermic reaction.

In the reaction

${{\rm{B}}_2} + {{\rm{C}}_2}\longrightarrow{{}}2{\rm{BC}}$

As B-C bond is weaker than B-B and C-C, this is an endothermic reaction.

In the reaction

${\rm{A}} + {\rm{BC}}\longrightarrow{{}}{\rm{AB + C}}$

As A-B bond is stronger than B-C, this is an exothermic reaction.

In the reaction

${{\rm{A}}_2} + {{\rm{B}}_2}\longrightarrow{{}}2{\rm{AB}}$

As A-B bond is stronger than A-A and B-B, this is an exothermic reaction.

In the reaction

${\rm{AB}} + {\rm{C}}\longrightarrow{{}}{\rm{AC}} + {\rm{B}}$

As A-C bond is weaker than A-B, this is an endothermic reaction.

Ans:

The endothermic reactions are as follows

$\begin{array}{l}\\{{\rm{A}}_2} + {{\rm{C}}_2}\longrightarrow{{}}2{\rm{AC}}\\\\{{\rm{B}}_2} + {{\rm{C}}_2}\longrightarrow{{}}2{\rm{BC}}\\\\{\rm{AB}} + {\rm{C}}\longrightarrow{{}}{\rm{AC}} + {\rm{B}}\\\end{array}$ .

The exothermic reactions are as follows

$\begin{array}{l}\\{\rm{A}} + {\rm{BC}}\longrightarrow{{}}{\rm{AB + C}}\\\\{{\rm{A}}_2} + {{\rm{B}}_2}\longrightarrow{{}}2{\rm{AB}}\\\end{array}$