Enthalpy vs. Entropy — What's the Difference?

A property of a system that combines internal energy and pressure-volume work.

Measures the randomness or unpredictability in a system.

Indicates whether a reaction is endothermic or exothermic.

Used to determine the feasibility and spontaneity of a process.

Used to calculate heating and cooling in physical and chemical changes.

A thermodynamic quantity indicating system disorder.

Reflects the heat exchanged in a chemical process at constant pressure.

Crucial for understanding the Second Law of Thermodynamics.

Integral to the First Law of Thermodynamics in expressing energy conservation.

Affects the efficiency of heat engines and refrigerators.

Enthalpy (listen) is a property of a thermodynamic system, and is defined as the sum of the system's internal energy and the product of its pressure and volume. It is a state function used in many measurements in chemical, biological, and physical systems at a constant pressure, that is conveniently provided by the large ambient atmosphere.

Entropy is a scientific concept, as well as a measurable physical property that is most commonly associated with a state of disorder, randomness, or uncertainty. The term and the concept are used in diverse fields, from classical thermodynamics, where it was first recognized, to the microscopic description of nature in statistical physics, and to the principles of information theory.

Symbol H A thermodynamic function of a system, equivalent to the sum of the internal energy of the system plus the product of its volume multiplied by the pressure exerted on it by its surroundings.

Symbol S For a closed thermodynamic system, a quantitative measure of the amount of thermal energy not available to do work.

A measure of the heat content of a chemical or physical system.

A measure of the disorder or randomness in a closed system.

(thermodynamics) a thermodynamic quantity equal to the internal energy of a system plus the product of its volume and pressure;

A measure of the loss of information in a transmitted message.

The tendency for all matter and energy in the universe to evolve toward a state of inert uniformity.

The deterioration of a system or society, especially when it seems inevitable

A measure of the disorder present in a system.

(Boltzmann definition) A measure of the disorder directly proportional to the natural logarithm of the number of microstates yielding an equivalent thermodynamic macrostate.

(information theory) Shannon entropy

A measure of the amount of energy in a physical system that cannot be used to do work.

The capacity factor for thermal energy that is hidden with respect to temperature.

The dispersal of energy; how much energy is spread out in a process, or how widely spread out it becomes, at a specific temperature.

A measure of the amount of information and noise present in a signal.

(uncountable) The tendency of a system that is left to itself to descend into chaos.

A certain property of a body, expressed as a measurable quantity, such that when there is no communication of heat the quantity remains constant, but when heat enters or leaves the body the quantity increases or diminishes. If a small amount, h, of heat enters the body when its temperature is t in the thermodynamic scale the entropy of the body is increased by h ÷ t. The entropy is regarded as measured from some standard temperature and pressure. Sometimes called the thermodynamic function.

(communication theory) a numerical measure of the uncertainty of an outcome;

(thermodynamics) a thermodynamic quantity representing the amount of energy in a system that is no longer available for doing mechanical work;

Enthalpy is used in calculating the energy requirements for heating and cooling systems, and in assessing reaction heat in chemical engineering.

Entropy quantifies the number of microscopic configurations that correspond to a macroscopic state, with higher entropy reflecting greater disorder.

Increased entropy in industrial processes often leads to greater energy dispersal, which can affect environmental energy flows and sustainability.

Enthalpy is a measure of energy conservation under constant pressure, while entropy provides a criterion for energy dispersal in a system.

Yes, negative enthalpy and positive entropy changes often indicate a reaction will proceed spontaneously.

Enthalpy changes describe the energy absorbed or released during phase changes, such as melting, vaporization, or condensation.

The sign of the enthalpy change; a negative ΔH indicates an exothermic process, and a positive ΔH indicates an endothermic process.

Entropy in biological systems is important for understanding energy flow, organization, and the evolution of complex systems.

Entropy increases with temperature as the molecular motion and disorder within a system increase.

In practical terms, entropy tends to increase; however, it can be locally decreased at the expense of greater increases elsewhere, consistent with the Second Law.

A common misconception is that entropy implies total chaos; rather, it quantifies dispersal of energy and probability of states in a structured manner.

Understanding entropy is crucial for designing more efficient systems that minimize energy waste, such as in computing and thermodynamic machines.

The increase in universal entropy leads to predictions about the "heat death" where no more useful energy will be available.

Enthalpy is measured in Joules, while entropy is measured in Joules per Kelvin.

Enthalpy represents the total energy flow in a system, including both heat transfer and work done, underpinning energy conservation principles.