Chapter 17.4, Problem 39LC

Interpretation Introduction

Interpretation: The method to calculate the standard heat of the reaction is to be explained.

Concept introduction: The standard enthalpy of the reaction or standard heat of the reaction occurs in a system where one mole of the matter is converted through a chemical reaction.

Answer to Problem 39LC

The standard heat of the reaction can be calculated by subtracting the sum of the standard enthalpies of the formation of the reactants from the sum of the standard enthalpies of the formation of the products.

Explanation of Solution

Calculating the standard heat of the reaction requires taking the sum of the standard enthalpies of the formation of the reactants (multiplying each by its stoichiometric coefficient) and subtracting it from the sum of the standard enthalpies of the formation of the products (multiplying each by its stoichiometric coefficient).

The formula to calculate the standard heat of the reaction is as follows:

  $\Delta H^{\circ }={\displaystyle \sum a_{\text{i}}}\Delta H_{\text{f}}^{\circ }\left(\text{products}\right)-{\displaystyle \sum b_{\text{i}}}\Delta H_{\text{f}}^{\circ }\left(\text{reactants}\right)$

Where,

• $\Delta H^{\circ }$ is the standard heat of the reaction.
• $\Delta H_{\text{f}}^{\circ }$ is the standard enthalpy of the formation.
• $a_{\text{i}}$ and $b_{\text{i}}$ are the stoichiometric coefficients.

Conclusion

The standard heat of the reaction can be calculated by subtracting the sum of the standard enthalpies of the formation of the reactants from the sum of the standard enthalpies of the formation of the products.