Chapter 17.4, Problem 37LC

Interpretation Introduction

Interpretation: Two methods that can be used to determine the heat of the reaction when it cannot measure directly are to be explained.

Concept introduction: Heat of reaction, or enthalpy of reaction, is the change in enthalpy of a chemical reaction under constant pressure. It is a thermodynamic unit helpful for determining the amount of energy per mole that is either released or created during a chemical process.

Answer to Problem 37LC

The two methods to determine the heat of the reaction indirectly are as follows:

1. Hess's law of heat summation
2. Standard heat of formation

Explanation of Solution

The two methods to determine the heat of the reaction when it cannot measure directly are as follows:

1. Hess's law of heat summation: Hess's law of heat summation allows for the indirect determination of the heat of a reaction by using the known heat of two or more chemical equations that can combine to provide the final reaction.
2. Standard heat of formation: Standard heat of formation of a compound is the change in enthalpy resulting from the production of one mole of a compound from its elements. Indirectly calculating the heat of the reaction is possible using standard heats of formation.

Conclusion

The two methods to determine the heat of the reaction indirectly are as follows:

1. Hess's law of heat summation
2. Standard heat of formation