Enter the total number of moles, initial volume, and final volume of an ideal gas into the calculator to determine the change in Entropy. This calculator can also determine the number of moles or either volume given the value of the other variables.

Entropy Formula

The following equation is used to calculate the change in entropy of an ideal gas.

E = n * R * ln(v2/v1)
  • Where E is the change in Entropy (J/K)
  • n is the number of moles
  • R is the gas constant (8.3145 J/mol*K)
  • v1 and v2 are the initial and final volumes respectively

To calculate entropy, multiply the number of moles by the gas constant, then multiply the result by the result of the natural log of the final volume divided by the initial volume.

Entropy Definition

Entropy is defined as the resistance of a substance to convert thermal energy into mechanical work.

Entropy Example

How to calculate entropy

  1. First, determine the number of moles.

    Calculate the number of moles of the ideal gas being analyzed.

  2. Next, measure the initial volume.

    Calculate or measure the initial volume of the gas.

  3. Next, measure the final volume.

    Measure the final volume after the reaction or change.

  4. Finally, calculate the change in entropy

    Calculate the change in entropy using the information from steps 1-3 and the formula above.


What is Entropy?

Entropy is a measure of energy per unit of temperature. In more specific terms, it’s a measure of the unavailability of the system to convert thermal energy into mechanical work.

How do you calculate Entropy?

Entropy is typically measured as a change in entropy using the formula above. The formula only applies to ideal gases.