The key difference between enthalpy and molar enthalpy is that enthalpy is the total heat content of a thermodynamic system, whereas molar enthalpy is the total heat per mole of reactant in the system.
Enthalpy and molar enthalpy are useful terms in physical chemistry for the determination of total heat content in a thermodynamic system. We can define a thermodynamic system as a body of matter or radiation which is confined by walls having certain permeabilities that can separate this system from the surrounding.
CONTENTS
1. Overview and Key Difference
2. What is Enthalpy
3. What is Molar Enthalpy
4. Enthalpy and Molar Enthalpy in Tabular Form
5. Summary – Enthalpy vs Molar Enthalpy
What is Enthalpy?
Enthalpy of a system is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. Therefore, it is a thermodynamic property of a system.
The equation of enthalpy is given below.
H = U + PV
In the above equation, H is the enthalpy of the system, U is the internal energy of the system, P is the pressure, and V is the volume. The enthalpy of a system is the indication of that system’s capacity to release heat (to do non-mechanical work). The enthalpy is denoted by the symbol H.
Figure 01: An Enthalpy Diagram showing the Enthalpy Changes for a Particular Chemical Reaction
Determining the enthalpy of a system allows us to indicate if a chemical reaction is exothermic or endothermic. The change in enthalpy of a system can be used to determine the heat of reactions and to predict if a chemical reaction is spontaneous or non-spontaneous.
What is Molar Enthalpy?
Molar enthalpy is the enthalpy value given per mole. In this definition, enthalpy is a thermodynamic quantity equivalent to the total heat content of a system. It is equal to the internal energy of the system plus the product of pressure and volume. The unit of measurement for this value is KJ/mol. Therefore, we can derive the equation for the determination of molar enthalpy as follows:
Molar enthalpy = DH/n
Where DH is the change in enthalpy of the system, “n” is the number of moles of reactant involved in the system. For example, molar enthalpy for the formation of a particular substance is the change in enthalpy when one mole of chemical species is formed in the standard state at a specified temperature. This formation of the substance occurs from the most stable form of the constituent chemical elements of that substance in their standard state.
What is the Difference Between Enthalpy and Molar Enthalpy?
Enthalpy and molar enthalpy are useful terms in physical chemistry for the determination of total heat content in a thermodynamic system. The key difference between enthalpy and molar enthalpy is that enthalpy is the total heat content of a thermodynamic system, whereas molar enthalpy is the total heat per mole of reactant in the system. Moreover, the unit of measurement for enthalpy is joules or kilojoules, while the unit of measurement for molar enthalpy is kilojoules per mole.
The following table summarizes the difference between enthalpy and molar enthalpy.
Summary – Enthalpy vs Molar Enthalpy
Enthalpy and molar enthalpy are useful terms that help to determine the total heat content in a thermodynamic system. Enthalpy of a system is a thermodynamic quantity equivalent to the total heat content of a system. Molar enthalpy is the enthalpy value given per mole. Therefore, the key difference between enthalpy and molar enthalpy is that enthalpy is the total heat content of a thermodynamic system, whereas molar enthalpy is the total heat per mole of reactant in the system.
Reference:
1. “Molar Enthalpy.” An Overview | ScienceDirect Topics, .
2. “What Is Enthalpy? – Definition, Endothermic & Exothermic Reaction.” BYJU’S, 16 Nov. 2020.
3. “Enthalpy.” Chemistry LibreTexts, Libretexts, 15 Aug. 2020.
Image Courtesy:
1. “Enthalpy-Diagram-Solution-Formation-Exothermic” By Dale J. Brugh – Own work (CC BY-SA 4.0) via Commons Wikimedia