Chapter 17, Problem 64A

Interpretation Introduction

Interpretation: Hess’s law of heat summation is to be explained.

Concept Introduction: Hess’s law is used to calculate the enthalpy of a reaction as the desired enthalpy is obtained by adding intermediate reactions together.

Answer to Problem 64A

Hess's law of heat summation Law states that at a constant temperature, the enthalpy change for a chemical reaction is the same regardless of the path by which the reaction occurs.

Explanation of Solution

Hess’ law is based on the state function character of enthalpy and the first law of thermodynamics. The enthalpy of a system is a state function. Thus, we can say that the enthalpy of reactant and product molecules is constant and does not change with the origin and path of formation.