Question

Gas A₂ reacts with gas B₂ to form gas AB at constant temperature. The bond energy of AB is much greater than that of either reactant. What can be said about the sign of ΔH? ΔS_surr? ΔS? Explain how potential energy changes for this process. Explain how random kinetic energy changes during the process.

Short answer

When a Gas A₂ reacts with gas B₂ to form gas AB at constant temperature and the bond energy of AB is much greater than that of either reactant then ΔH increases, ΔS decreases, ΔS_surrdecreases, potential energy increases and kinetic energy decreases.

Step-by-step solution

ΔH of reaction  

As given in the question that bond energy of the product that is AB is greater than the bond energies of the either of the reactants. So, ΔH of the reaction is positive.

${\mathbf{\Delta H}}_{\mathbf{reaction}}\mathbf{=}\mathbf{+}\mathbf{ve}$

In any endothermic reaction, the energy is stored in the form of the potential energy, hence potential energy also increases.

Definition of Entropy

As the bonds in the product that is AB is stronger than the bond of the either of the reactants so the molecules are now more restricted to move as compared to earlier so ΔS decreases means

$\mathbf{\Delta S}\mathbf{=}\mathbf{-}\mathbf{ve}$

As in the process potential energy increases means energy flow from surroundings to the system.

${{\mathbf{\Delta S}}_{\mathbf{sur}}}_{\mathbf{r}}\mathbf{=}\mathbf{-}\mathbf{ve}$

As the molecules are now more restricted to move means kinetic energy has been reduced.