Entropy Calculator

Entropy Change Calculator

Compute ΔS = Q_rev / T for reversible heat transfer.

2026-05-06T10:07:27.206Z
J
K

Entropy Change (ΔS)

3.3540 J/K

0.003354 kJ/K

Formula: ΔS = Q_rev / T

What is Entropy?

Entropy measures the dispersal of energy in a system; for a reversible transfer at constant temperature, ΔS = Q_rev / T. It is a state function and central to the second law of thermodynamics.

This calculator provides a simple reversible-process estimate. For temperature-dependent or irreversible processes, more advanced thermodynamic analysis is required.

How to Use

  1. Enter reversible heat transfer Q_rev in joules.
  2. Enter temperature in kelvin (T > 0).
  3. Read ΔS in J/K and kJ/K; for molar ΔS divide by moles.
  4. Use latent heats for phase transitions at constant T when appropriate.
  5. Combine with other thermodynamic relations for more complex processes.

Worked Example

Given: Q_rev = 500 J, T = 300 K
Step: ΔS = 500 / 300 = 1.666667 J/K
Result: 1.666667 J/K

Frequently Asked Questions

What is entropy change?

For a reversible heat transfer, ΔS = Q_rev / T where T is absolute temperature in kelvin.

What units are used?

This tool shows ΔS in J/K and kJ/K.

Why must T > 0?

Absolute temperature in kelvin must be positive; division by zero or negative temperatures are invalid for this formula.

Is this for irreversible processes?

No — formula applies to reversible transfers; irreversible processes require path-dependent analysis.

How to use molar entropy?

To get molar ΔS, divide ΔS by number of moles involved.

What about phase changes?

For phase changes, use latent heat at the transition temperature; integrate when temperature varies.

Any safety notes?

This is a math tool — verify thermodynamic assumptions before using for design.

Why include kJ/K?

kJ/K provides a compact, human-friendly scale for large energy transfers.

Formula: ΔS = Q_rev / T. Use absolute temperature (K) and reversible heat transfer.

Related Tools