Question

Can you please explain how to use bond energies to determine the change in heat for reactions.

Answer 1

Hint: When we use bond energies to calculate heats of reaction, we use Hess law. The general information about the Hess law can help us solve the illustration properly. Bond energy is also known as bond enthalpy.

Complete step by step solution:
Let us study the Hess law in detail;
Bond energy or enthalpy is the energy required per mole of gaseous compound to break a particular bond. This breakage needs energy and hence, breaking of a bond is considered as an endothermic reaction. Whereas, simultaneously the bond formation will take place in the same environment. This is the exothermic reaction as this releases energy.
The bond energies are used to determine the heat of reaction as;
$\Delta H{}^\circ \left( reaction \right)$ = sum of the bond energies of bonds being broken – sum of bond energies being formed
$\Delta H{}^\circ \left( reaction \right)$ = $\sum{{{H}_{\left( reac\tan t \right)}}-\sum{{{H}_{\left( product \right)}}}}$ __________________ Hess’s law.
Steps to calculate the heat of reaction using above given equation are;
Step I- Write the balanced chemical equation to properly determine the stoichiometric coefficients and make it feasible for further calculations.
Step II- Write the general equation for heat of reaction and substitute the given bond energies to calculate the same.

Note: Do note that all the reactants and products need to be in gaseous state to use the Hess law and calculate heat of reaction from the given bond energies. Also, take care of the units and signs while we solve the actual problem statement about the bond energies and heat of reaction.