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:
\(\ ΔS_{reaction} = \ ΔS_{products} − ΔS_{reactants}\)
\(\ ΔS_{reaction} = \ 20 − 30\)
\(\ ΔS_{reaction} = \ -10\)
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