Chapter 7, Problem 94E

Interpretation Introduction

Interpretation:

The enthalpy of combustion for lactic acid should be determined.

Concept introduction:

The enthalpy of reaction can be determined by Hess’s law. According to this law, the enthalpy of a reaction is independent of the path taken and it depends on the initial reactants and final products.

The mathematical expression to calculate the enthalpy of reaction:

${\text{ΔH}}_{\text{r}}^{\text{0}}\text{=}{\displaystyle \sum {\text{H}}_{\text{f}}^{\text{0}}\text{(products)}}-{\displaystyle \sum {\text{H}}_{\text{f}}^{\text{0}}\text{(reactants)}}$

${\text{ΔH}}_{\text{r}}^{\text{0}}\text{= [c }\times {\text{ H}}_{\text{f}}^{\text{0}}\text{(C) + d }\times {\text{ H}}_{\text{f}}^{\text{0}}\text{(D)]-[a }\times {\text{ H}}_{\text{f}}^{\text{0}}\text{(A) + b}\times {\text{ H}}_{\text{f}}^{\text{0}}\text{(B)]}$

This relation can be used for determination of enthalpy of formation of any compound if the heat of reaction and enthalpy of formation of other compounds are given.