Entropy Change Calculator

Understanding Entropy Change Calculator

Entropy is a measure of disorder in a system. For reversible heat transfer at constant temperature, the entropy change equals heat divided by temperature.

How to use this calculator

1. Enter the heat transferred, \(Q\), using joules, \(\mathrm{J}\).
2. Enter the constant temperature, \(T\), using kelvin, \(\mathrm{K}\).
3. Check that the temperature is not zero, because \(\Delta S = \frac{Q}{T}\) would be undefined.
4. Compute the entropy change, \(\Delta S\), in \(\mathrm{J/K}\).

The formula explained

The formula \(\Delta S = \frac{Q}{T}\) computes the entropy change when a quantity of heat \(Q\) is transferred at constant temperature \(T\). A positive \(Q\) gives a positive entropy change, and a negative \(Q\) gives a negative entropy change.

• \(\Delta S\) = entropy change, in \(\mathrm{J/K}\)
• \(Q\) = heat transferred, in \(\mathrm{J}\)
• \(T\) = constant temperature, in \(\mathrm{K}\)

Step by step method

1. Write down the heat transferred \(Q\) and the constant temperature \(T\).
2. Substitute the values into \(\Delta S = \frac{Q}{T}\).
3. Divide \(Q\) by \(T\) to get the entropy change.
4. State the answer with units of \(\mathrm{J/K}\).

Worked example

Problem. A system absorbs \(500\,\mathrm{J}\) of heat at a constant temperature of \(250\,\mathrm{K}\). Find the entropy change.

1. Use \(\Delta S = \frac{Q}{T}\).
2. Substitute the values, \(\Delta S = \frac{500}{250}\).
3. Compute \(\Delta S = 2\,\mathrm{J/K}\).

Tips and common mistakes

• Make sure temperature is in kelvin, not degrees Celsius.
• If the system releases heat, use a negative value for \(Q\), so the entropy change will be negative.

Frequently asked questions