The key difference between enthalpy and entropy is that enthalpy refers to the overall heat content within a system, whereas entropy characterizes the level of disorder or randomness within that system.
What Is Enthalpy?
Enthalpy serves as a crucial thermodynamic property that quantifies the total heat exchange within a system. According to the First Law of Thermodynamics, it is the sum of internal energy and the product of pressure and volume.
Directly determining the system’s total enthalpy can be challenging due to unknown internal energy parameters. Instead, we focus on measuring enthalpy changes to better understand processes. Mathematically, this can be expressed as:
H = U + PV
In this equation, U represents internal energy, P is pressure, and V denotes volume. Additionally, assessing the change in enthalpy helps identify whether a reaction is endothermic (absorbs heat) or exothermic (releases heat). Notably, the sequence or number of reaction steps does not influence the enthalpy change value.
What Is Entropy?
Entropy is a measurable physical property that reflects the level of disorder within a system composed of molecules, whether it’s a solid or a fluid. When molecules are more disordered and random, entropy increases, and the potential for converting heat into work diminishes. Initially referred to as ‘heat potential,’ Clausius later defined entropy as the ratio of a small change in heat to the instantaneous temperature in a reversible process:
ΔS = ΔQ / T
Lower molecular randomness results in lower entropy, making solids typically possess less entropy than fluids. It’s important to note that the total entropy of a system and its surroundings always increases, signifying that the entropy of the universe continually rises.
Enthalpy vs Entropy
The important difference between enthalpy and entropy is given below:
| Parameter | Enthalpy | Entropy |
| Nature | It is a kind of energy. | It is property of the matter. |
| Definition | It is the sum total of the internal energy and energy flow. | It is scientific measurement of the randomness of molecules. |
| System tendency | The natural system always favors the minimum enthalpy. | The natural system favors maximum entropy. |
| Nomenclature | This term was given by scientist Heike Kamerlingh Onnes. | This term was given by scientist Rudolf Clausius. |
| Standardization | It is applicable to the related standard conditions. | It does not have any specified limit or condition. |
| Unit of measurement | Its unit is Joule per mol. | Its unit is Joule per Kelvin. |
| Symbol | Its symbol is H. | Its symbol is S. |