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Entropy Calculator

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

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?

• 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:

$$\ ΔS_{reaction} ​= \ ΔS_{products} ​− ΔS_{reactants}​$$

$$\ ΔS_{reaction} ​= \ 20 ​− 30​$$

$$\ ΔS_{reaction} ​= \ -10​$$