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?

“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.

Where

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:

\(\ ΔS = n*R*ln\ (\dfrac{P_2}{P_1})\)

Where

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

where,

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

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

Solution:

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

\(\ ΔS_{reaction} = \ 20 − 30\)

\(\ ΔS_{reaction} = \ -10\)