Enthalpy vs Entropy – Difference Between Enthalpy and Entropy

The difference between enthalpy and entropy is that enthalpy is a measurement of the total amount of heat contained by a system at any one time, whereas entropy measures the extent of change taking place within a chemical reaction.

These terms are regularly discussed and used as part of thermodynamic study (the movement of heat), but due to their similar pronunciation, they are frequently confused with one another.

Today, we are going to totally clear up the variations between enthalpy vs entropy so that you can walk away with a clear understanding of which one is which. If you are ready to find out more, read on.

Definition of Enthalpy – So What Is Enthalpy?

The definition of enthalpy is the total amount of heat contained in a system or reaction.

The first major difference between enthalpy and entropy can be found when reading the above definition. This is because the former measures the exact amount of heat contained by a system or reaction as a whole as opposed to measuring any heat and movement variations that occur within the separate molecules of a system or reaction (which is where the latter comes into play).

Even though the heat dynamics can alter when we are studying enthalpy, ultimately, we are still measuring heat as a whole unit rather than breaking it down and observing its constituents. For example, the main difference between entropy and enthalpy is that we are specifically observing the exact nature and value of constant molecular change with entropy.

With enthalpy, we are observing what happens after change occurs. Once a reaction has taken place, we are then analyzing the impact that the reaction has had on the total heat available in a system. When we are observing static enthalpy, we are observing the total value of heat in a system that does not change.

Another way that we could describe enthalpy would be as available energy potential. When we are studying this element of thermodynamics, we are quite literally trying to determine how much available energy or heat the entire system has at its disposal and therefore how much movement or activity it is capable of creating as a result.

We commonly measure enthalpy in joules or calories. These measurements give us a realistic overview of the total available energy expenditure we have accessible at any one time in our bodies to perform basic movement and actions.

Enthalpy does not specifically have to relate to the human body. This is just the most common example of where we will encounter it in action every day. Whenever we calorie count, we are trying to determine the overall enthalpy of our bodies. This helps us to measure our energy expenditure in relation to everything from performing physical activity to burning excess body fat if required.

The word enthalpy originated in Greece and is taken from the word “enthalpos” meaning “to put heat into.” The term was originally used by the scientist Kamerlingh Ommes. The formula for enthalpy is H (enthalpy) = E (internal energy) + P (pressure) V (volume). Its symbol is “ΔH.”

With enthalpy, we are measuring the overall value of a static element of heat or a heat exchange. What we are not doing is observing the individual molecular movements that lead to that change occurring. This is where entropy comes into play.

Definition of Entropy – So What Is Entropy?

The definition of entropy is the level of molecular disorder or sporadic and random activity taking place within a chemical reaction.

The difference between entropy and enthalpy is clear as day once you fully understand the definition of enthalpy. Essentially, enthalpy is the total value of heat. Entropy on the other hand is all about the activity that takes place in the midst of chemical reactions that leads to heat or other changes.

Enthalpy could be described more as an end result, whereas entropy could be described as a process leading to an end result. For example, if we were to measure the total amount of heat contained by a furnace in a static state, this would be enthalpy.

Once we had added more fuel to the furnace in the form of logs (for example), the additional heat we managed to generate would create a new value. This value would again be enthalpy. Though the value of heat would change, the metric would remain the same as we would still be measuring overall heat value.

If we were observing the entropy of the same process, we would be observing the nature of the changes that were occurring in order to lead to the heat increase. So, once we had added the logs to the furnace, we would be observing them at a molecular level to see how they were breaking down and what the separate molecules were doing in order to create more heat.

The more activity and randomness that occurs within any one process, the more entropy that is then created as a result. It is accepted that the more static the molecules are in a particular reaction, the further away they are from being stable. This is because randomness needs to occur in order to create change and thus reach a conclusive end result.

In other words, the more entropy that occurs, the more stable and continuous a chemical process can be. Log burning is a prime example because without the introduction of more entropy through the addition of more logs, a stable heat and state of enthalpy cannot be reached. In this sense, enthalpy and entropy work in perfect synergy with one another.

Entropy finds its origins in Greece, with the term “en-trope,” which is loosely translated as “inside transformation.” The term as we know it was originally used by the scientist Rudolf Clausius. The formula for entropy is S (entropy) = K♭ (Boltzmann constant) In (natural logarithm) Ω (the quantity of microscopic configurations). The symbol for entropy is “S.”

In the next section, we will lay out the variations between enthalpy vs entropy in a quick reference table.

What Is the Main Difference Between Enthalpy vs Entropy?

Here are the key variations between entropy vs enthalpy.

Term	Enthalpy	Entropy
Measuring	Overall heat value	Molecular change leading to an end result
Nature	An end result	A process leading to an end result
Originates from the word	Enthalpos	En-trope
Meaning	To put heat into	Inside transformation
First mentioned by	Kamerlingh Ommes	Rudolf Clausius.
Examples	The number of calories or joules contained by a human body before or after food consumption	The breakdown of food to create calories and the molecular changes occurring as part of the breakdown process
Unit of measurement	Typically measured in calories and/or joules	Typically measured in joules
Formula	H = E + PV.	S = K♭ In Ω.
Symbol	ΔH	S

Any time you get stuck trying to separate entropy vs enthalpy, come back to this quick reference table for a refresh.

Entropy and Enthalpy – FAQ

We will now provide you with the answers to the most frequently asked questions about these two thermodynamic terms.

Q: Are entropy and enthalpy the same?

A: No, entropy measures the randomness of chemical reactions leading to heat changes, whereas enthalpy measures the overall heat value of a system after, during, or before any kind of change or chemical reaction.

Q: So, what is entropy, and how do I measure it?

A: Entropy isthe measure of change taking place at a molecular level within any one chemical reaction, and we can measure this change by observing the degree of movement and randomness occurring between the individual molecules of said reaction.

Q: So, what is enthalpy, and how do I measure it?

A: Enthalpy is the exact amount of heat contained within a system at any one time during, before, or after some kind of molecular change has occurred. Most commonly, enthalpy is measured using calories or joules.

So What Is the Difference Between Entropy and Enthalpy? – Conclusion

You should finally be able to summarize these two thermodynamic terms with ease after reading through their individual definitions.

Just remember that if you want to provide an easy summary of each, then entropy directly measures the amount of change taking place within a chemical reaction whereas enthalpy measures the overall amount of heat contained within a system.

You can also come back to the quick reference table we provided earlier for a visual overview of their differences without having to read through the deeper explanations of each word again.