Chapter EN, Problem 8PQ

Interpretation Introduction

Interpretation:

$\Delta H$ for following gas phase reaction has to be determined.

  ${\text{NH}}_3\left(g\right)+{\text{Cl}}_2\left(g\right)\to {\text{NH}}_2\text{Cl}\left(g\right)+\text{HCl}\left(g\right)$

Concept Introduction:

Heat released or absorbed in a chemical reaction due to the difference in the bond energies (BE) of reactants and products in the reaction is known as the heat of reaction. It is represented by $\Delta H_{\text{reaction}}$.

The heat of reaction $\left(\Delta H_{\text{reaction}}\right)$ can have two values: If the reaction is endothermic, more energy needs to be supplied to the system than that released by it. So $\Delta H_{\text{reaction}}$ comes out to be positive. If the reaction is exothermic, more energy is released by the system than that supplied to it. So $\Delta H_{\text{reaction}}$ comes out to be negative.

The formula to calculate heat of reaction is,

  $\text{Δ}{H}_{\text{reaction}}=\sum {\text{BE}}_{\text{reactant bond broken}}-\sum {\text{BE}}_{\text{product bond formed}}$

Here,

  $\Delta H_{\text{reaction}}$ is heat of reaction.

  ${\text{BE}}_{\text{product bond formed}}$ is bond energy of bond formation in products.

  ${\text{BE}}_{\text{reactant bond broken}}$ is bond energy of bond breakage in reactants.