Created By : Rina Nayak

Reviewed By : Rajashekhar Valipishetty

Last Updated : Apr 03, 2023

Entropy is all about the disorder, this free Entropy Calculator is helpful to find the change in entropy for a reaction, change in Gibbs free energy and change in entropy of isothermal ideal gas. All you need to do is enter the required details in the input fields of the Entropy Change Calculator and hit the calculate button to obtain the answer quickly.

Entropy change for a reaction

Total Entropy Of Products
Total Entropy Of Reactants
Entropy Change of a reaction

Gibbs free energy ΔG = ΔH - T*ΔS

Change in enthalpy
Change in entropy
Change in Gibbs free energy

Isothermal entropy change of an ideal gas

Base variable
Amount of moles
Initial Pressure
Final Pressure
Change in entropy

How to Calculate Entropy Change?

Go through the simple and easy guidelines to find the chane in entropy of an object

Entropy Change for a Reaction

  • Know the total entropy of products, the total entropy of reactants.
  • Subtract the total entropy of products from the total entropy of reactants to get the entropy change of a reaction.

Gibbs Free Energy

  • Obtain the change in enthalpy, temperature and change in entropy deatils.
  • Multiply the temperature by change in entropy.
  • Subtract it from the change in enthalpy to get the Gibbs free energy.

Isothermal Change in Entropy of an ideal gas

  • Check the number of moles, initial volume, final volume.
  • Divide the final volume by the initial volume.
  • Get the log of the answer.
  • Multiply it by the universal gas constant and amount of moles to see the entropy change value.

What is Entropy?

Entropy is a mesaure of disorderness or chaos. According to the seond law of thermodynamics, the disorder of a system is always increasing. It is not posiible to measure the entropy physically, but we can calculate it. It is the main determinants of the spontaneity of a reaction.

The concept of entropy wsa introduced by a German physicist named Rudolf Clausis in the year 1850. The important definitions of entropy include thermodynamic definition and statistical definition. In the view of thermodynamics, entropy is used to describe the behaviour of the system like pressure, temperature, and heat capacity.

Any spintaneous process that increases the disorder of the universe is the entropy. The entropy of a system is connceted to systems energy.

Entropy Change for a Reaction

Entropy depends on the initial and final states of a system. It is the difference between the entropy of products and reactants.

For a chemical reaction, the change in entropy formula is

ΔSreaction = ΔSproducts - ΔSreactants

It can also be written as ΔS°reaction = ΔS°products - ΔS°reactants


S is the entropy

S° is the standard entropy

ΔSreaction is the change in entropy of reaction

ΔSproducts is the entropy change in products

ΔSreactants is the entropy change in reactants

The standard entropy values of some of the chemical substances are listed here:

Substance Standard Entropy
H2 (gas) 131.0
O2 (gas) 205.0
H2O (gas) 188.7
H2O (liquid) 69.9
C (diamond) 2.4

Gibbs Free Energy Equation

Gibbs free energy equation evaluates the energy available in a system to do work on surroundings at a constant pressure and temperature. It is used to predict the spontaneity of a process. The equation is

ΔG = ΔH - (T * ΔS)


ΔG is the chnage in Gibbs free energy

ΔH is the change in enthalpy

ΔS is the change in entropy

T is the temperature

Isothermal Entropy Change of an Ideal Gas | Entropy Change Formula

For the isothermal process of ideal gas, entropy for pressure and volume can be as follows:

ΔS = n * R * ln(V₂/V₁) = - n * R * ln(P₂/P₁)


n is the number of moles

R is the universal gas constant, 8.3145 J/Kmol

V₁, V₂ is the initial and final volume

P₁, P₂ is the initial and final pressure

If you would like to learn more about the other chemistry calculator that gives instant results, stay tuned to Chemistrycalc.Com

Frequently Asked Question’s on Entropy Calculator

1. What is a simple definition of entropy?

Entropy is a measure of randomness or disorder of a system. It can be explained in thermodynamics and statistics. The second law of thermodynamics states that the disorder of a system is always increasing.

2. What does Shannon entropy measure?

The Shannon entropy measures the entropy of an object or the system is a measure of the randomness in the system.

3. How to calculate the change in entropy?

The change in entropy measures the difference between the entropy of products and reactants. The entropy change formula for chemical reactions is ΔSreaction = ΔSproducts - ΔSreactants. The Gibbs free energy equation is ΔG = ΔH - (T * ΔS) and isothermal entropy change of an ideal gas is ΔS = n * R * ln(V₂/V₁) = - n * R * ln(P₂/P₁). Substitute the values in the formulas and solve the equation to get the result.


4. What are the properties of entropy?

The entropy properties are listed here:

  • Entropy is a thermodynamic function.
  • It is a state function that depends on the state of the system.
  • Entropy is an extensive property which means that it scales with zero or extent of the system.
  • SI unit is J/Kmol.

5. What is entropy change?

Entropy change can be defined as the change in the state of disorder of the thermodynamic system that is associated with the conversion of heat into work.

Entropy Calculator