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Chapter 6: Problem 21

Define these terms: enthalpy, enthalpy of reaction. Under what condition is the heat of a reaction equal to the enthalpy change of the same reaction?

Short Answer

Expert verified
Enthalpy is the total energy in a thermodynamic system, which includes the internal energy plus the product of pressure and volume. Enthalpy of reaction or heat of reaction refers to the amount of heat that's released or absorbed during a chemical reaction at constant pressure. The heat of a reaction is equal to the enthalpy change of the reaction under the condition of constant pressure.

Step by step solution

01

Definition of Enthalpy

Enthalpy (\(H\)) is a thermodynamic potential that measures the total energy in a thermodynamic system, which is the sum of the internal energy and the product of pressure and volume. It can be written as: \(H = U + PV\), where \(U\) is the internal energy, \(P\) is the pressure, and \(V\) is the volume.
02

Definition of Enthalpy of Reaction

Enthalpy of reaction or heat of reaction, denoted as \(\Delta H\), refers to the amount of heat that's released or absorbed during a chemical reaction in constant pressure conditions. It can be calculated through the formula: \(\Delta H = H_{products} - H_{reactants}\), which reflects the difference in enthalpy of the products and the reactants.
03

Condition for Heat and Enthalpy Equivalence

The heat of reaction is equal to the enthalpy change of the reaction under constant pressure conditions. This is because at constant pressure, the system can do work by the expansion or contraction of gases in the substance, thereby causing the heat content or enthalpy to change. Hence, under these circumstances, the heat transferred in or out of the system is indicative of the change in the system's enthalpy.

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