Entropy Calculator

Entropy Calculator

Calculate the entropy change, and find whether a reaction is spontaneous or not through the following calculator by adding the required inputs.

I Want To Calculate:

Total Entropy Of Products:

j/mol*K ▾

Total Entropy Of Reactants:

j/mol*K ▾

Base Variable:

Amount Of Atom:

mol

Initial Volume:

mm³ ▾

Final Volume:

mm³ ▾

Entropy Calculator

The entropy calculator helps to estimate the entropy change of a chemical reaction in seconds. You can also determine the Gibbs free energy and isothermal entropy change of an ideal gas.

What Is Entropy In Chemistry?

“Entropy is a measurable physical property that is most commonly associated with uncertainty.”

Entropy represents the degree of disorder or randomness in a system. According to the second law of thermodynamics, the disorder of a system always tends to increase. Entropy quantifies this disorder.

Entropy is useful in determining whether a reaction is spontaneous. A spontaneous reaction occurs naturally without external energy input, whereas a non-spontaneous reaction requires energy from an external source. Using the entropy change along with Gibbs free energy, you can predict the spontaneity of chemical reactions.

Entropy Formula

The entropy change of a reaction is calculated as:

ΔS_reaction = ΔS_products - ΔS_reactants

Standard Entropy Values

The table below shows standard entropy values (S°) for some common substances, measured in joules per mole per kelvin (J/mol·K).

Substance	S° (J/mol·K)
Hydrogen (H₂)	130.7
Oxygen (O₂)	205.0
Carbon (C, graphite)	5.74
Water (H₂O, liquid)	69.91
Water (H₂O, vapor)	188.8
Methane (CH₄)	186.3
Ethanol (C₂H₅OH)	160.7
Sodium chloride (NaCl)	72.1
Nitrogen (N₂)	191.6
Carbon dioxide (CO₂)	213.7

Gibbs Free Energy Formula

ΔG = ΔH - (T × ΔS)

If ΔG < 0, the process is spontaneous.
If ΔG = 0, the system is in equilibrium.
If ΔG > 0, the process is non-spontaneous and requires additional energy.

Where:

ΔG = change in Gibbs free energy
ΔH = change in enthalpy
T = absolute temperature (K)
ΔS = change in entropy (J/mol·K)

Isothermal Entropy Change Formula

For Volume: ΔS = n × R × ln(V₂/V₁)

For Pressure: ΔS = n × R × ln(P₂/P₁)

Where:

n = number of moles of the gas
R = universal gas constant = 8.3145 J/mol·K
V₁, V₂ = initial and final volumes
P₁, P₂ = initial and final pressures

How To Calculate Entropy Change

Determine the initial and final states of the system (temperature, volume, pressure, etc.).
Substitute these values into the entropy change equation.

Entropy Change Example

Calculate the entropy change for a reaction:

ΔS_products = 20 J/mol·K
ΔS_reactants = 30 J/mol·K

Solution:

ΔS_reaction = ΔS_products - ΔS_reactants

ΔS_reaction = 20 - 30

ΔS_reaction = -10 J/mol·K