Enthalpy and Entropy are important concepts in thermodynamics that relate heat and work. Enthalpy can be defined as the total energy in a system, whereas entropy is defined as the thermal energy of a system per unit temperature. Thus the major difference between enthalpy and entropy is that enthalpy is a type or kind of energy of the system whereas entropy is only a property of the system as a whole.
In this article, we will learn about Enthalpy, Entropy, the Difference between Enthalpy and Entropy, and others in detail.
What is Enthalpy?
Enthalpy is the total amount of energy contained in the system. It can also be defined as the sum of the internal energy of the system and the product of pressure and volume of the system. The heat in a system may enter or leave a system. Thus enthalpy is an important factor in understanding the nature of chemical reaction.
If we denote enthalpy with H and internal energy, pressure and volume with U, P and V respectively, then the relation between them can be mathematically written as:
H = U + PV
If we use enthalpy change, internal change and volume change then the same equation can be written as:
ΔH = ΔU + PΔV
If enthalpy change is negative, then heat is given out and reaction is exothermic in nature whereas heat is absorbed if enthalpy change is positive and reaction is endothermic reaction.
Examples of Enthalpy
Various real life examples of enthalpy are as follows:
- The number of calories in food is estimated by the amount of energy released due to breaking of glucose bonds in the body.
- Efficiency of engines of automobiles are estimated with the help of enthalpy change.
- Enthalpy is also used to design the refrigerant compressors.
Read more about Enthalpies for Different Types of Reactions.
What is Entropy?
Entropy of a system represents the degree of randomness of a system. Higher the randomness of the molecules in a system, more is the entropy of the system. Thus gases have the highest entropy among 3 states of matter. Entropy may also be defined as the thermal energy of a system per unit temperature.
If we denote entropy by S, internal energy by Q and temperature by T, then relation between them can be mathematically represented as:
S = Q/T
If we use entropy change, internal energy change and temperature then the Entropy Change Formula is,
ΔS = ΔQ/T
Note: Entropy of the universe is always increasing.
Examples of Entropy
Some real life examples of entropy are as follows:
- The smoke of an incense cone always expands and spreads in the room which shows the increase in entropy.
- Universe always favors the process which increases entropy. For example, melting of ice is a natural phenomenon and happens on its own as it leads to increase in entropy of the ice when it changes from solid state to liquid state.
Enthalpy and Entropy
Relation between enthalpy and entropy can be mathematically expressed using Gibbs Helmholtz equation which is written as follows:
ΔG = ΔH - TΔS
Where,
- ΔG is the change in free energy,
- ΔH is the enthalpy change, and
- ΔS is the entropy change.
Note: ΔG is always negative for a spontaneous reaction.
Difference Between Enthalpy and Entropy
The key differences between Enthalpy and Entropy are listed in the following table:
| Basis Of Difference | Enthalpy | Entropy |
|---|
| Meaning | Enthalpy is the measure of the total energy contained in the system. | Entropy is defined as the degree of randomness in a system. |
|---|
| SI Units | Enthalpy is measured in Jmol-1 | It is measured in JK-1 |
|---|
| Symbol | It is denoted using symbol H | It is denoted using symbol S. |
|---|
| Formula | It is calculated using H = U + PV | It is calculated using S = Q/T |
|---|
| Scientist | Heike Kamerlingh Onnes coined the term enthalpy. | Rudolf Clausius coined the term entropy. |
|---|
| Spontaneity | Universe always favors reaction with low enthalpy. | Universe always favors reaction that increases the entropy. |
|---|
Examples | Combustion reactions, phase transitions (e.g., melting, boiling), etc. | Mixing of gases, dissolving solids in liquids, heat conduction, etc. |
|---|
Read More,
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