Chapter 15.4, Problem 39SSC

Interpretation Introduction

Interpretation:

The formula used to calculate enthalpy change in a reaction is to be explained.

Concept introduction:

According to Hess’s Law, if one equation is the resultant of two different equations then change in enthalpy of the equation is sum of enthalpy change of both reactions.

Answer to Problem 39SSC

According to law, enthalpy change of reaction is calculated by subtracting sum of enthalpy of products from sum of enthalpy of reactants.

Explanation of Solution

Standard enthalpy of a reaction is calculated by subtracting sum of heat of formation of reactants from sum of heat of formation of products.

$\Delta {{\rm H}}_{rxn}^0={\displaystyle \sum \Delta {{\rm H}}_f^0(products)-}{\displaystyle \sum \Delta {{\rm H}}_f^0(reac\tan ts)}$

Conclusion

Thus, Hess’s Law helps to calculate enthalpy change in the reaction.