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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:


Total Entropy Of Reactants:


Change In Enthalpy:




Change In Entropy:


Base Variable:

Amount Of Moles:


Initial Volume:



Final Volume:




Table of Content

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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?

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

In simple words, it’s the degree of disorder or uncertainty in a system. According to the second law of thermodynamics, the disorder of a system always increases. Entropy is the measure of this disorder.

Entropy is very helpful in determining the spontaneity of a reaction. A spontaneous reaction does not involve any outside energy to happen and on the other hand, a non-spontaneous requires some energy from the outside source. 

By using the entropy change and the Gibbs free energy you can determine the spontaneity of the chemical reactions. 

Entropy Formula:

The equation for entropy is outlined below:

\(\ ΔS_{reaction} ​= \ ΔS_{products} ​− ΔS_{reactants}​\)

Standard Entropy Values:

In the following table, we have mentioned some substances and their corresponding entropy values. Let’s take a look:

Substance \(\ S^\circ \,(\text{J/(mol}\cdot\text{K)}\)
\(\ Hydrogen\ (H_{2})\) 130.7
\(\ Oxygen\ (O_{2})\) 205.0
\(\ Carbon\ (C, graphite)\) 5.74
\(\ Water\ (H_{2}O,\ liquid)\) 69.91
\(\ Water\ (H_{2}O,\ vapor)\) 188.8
\(\ Methane\ (CH_{4})\) 186.3
\(\ Ethanol\ (C_{2}H_{5}OH)\) 160.7
\(\ Sodium\ chloride (NaCl)\) 72.1
\(\ Nitrogen\ (N_{2})\) 191.6
\(\ Carbon\ dioxide\ (CO_{2})\) 213.7

Gibbs Free Energy Formula:

ΔG = ΔH – (T * ΔS)

  • IF ΔG < 0 then it’s a spontaneous process
  • When ΔG = 0 it means the system is in equilibrium
  • IF ΔG > 0 it is a nonspontaneous process, you will have to provide additional energy for the happening of the process. 


  • ΔG shows the change in Gibbs free energy
  • ΔH represents a change in enthalpy
  • T is the temperature
  • ΔS is the representative of change in entropy.

Isothermal Entropy Change Formula:

For Volume:

\(\ ΔS = n*R*ln\ (\dfrac{V_2}{V_1})\)

For Pressure:

\(\ ΔS = n*R*ln\ (\dfrac{P_2}{P_1})\)


  • n shows the number of moles.
  • R represents the gas constant, which is 8.3145 J/mol*K
  • \(\ V_2​, V_1\)​ is the final and initial volume
  • \(\ P_2​, P_1\)​​ represent the final and initial pressure.

How To Calculate Entropy Change?

Follow the below outlined steps:

  • Determine the initial and final states of the system. These states revolve around the temperature, volume, pressure, or other related parameters 
  • Put the values of initial and final states in the entropy change equation as we have done below

Entropy Change Example:

Calculate Entropy change for a reaction 


\(\ ΔS_{products} = \ Total\ entropy\ of\ products\) = 20 J/mol*K

\(\ ΔS_{reactants} = \ Total\ entropy\ of\ reactants\) = 30 J/mol*K


\(\ ΔS_{reaction} ​= \ ΔS_{products} ​− ΔS_{reactants}​\)

\(\ ΔS_{reaction} ​= \ 20 ​− 30​\)

\(\ ΔS_{reaction} ​= \ -10​\)