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**Table of Content**

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.

**“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.

The equation for entropy is outlined below:

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

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 |

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.

**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.

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

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:**

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

\(\ ΔS_{reaction} = \ 20 − 30\)

\(\ ΔS_{reaction} = \ -10\)