Question

I know that for reversible processes: entropy change = dq/t Here its unit should J/Kelvin but it is mentioned in my books that its unit is J/Mol-Kelvin. I do not understand why there is mole in denominator of unit. Also, if J/mole-Kelvin is the unit, then why it is an extensive property? Extensive properties vary based on quantity, but this is strictly per mole.

Answer 1

The unit of entropy change in reversible processes includes moles in the denominator because entropy is an extensive property that depends on the amount of substance involved. Despite being an extensive property per mole, entropy is useful for comparing the disorderliness of substances and predicting spontaneity.

Step-by-step explanation:

The unit of entropy change can be expressed as J/mol-Kelvin because entropy is an extensive property that depends on the amount of substance present. When we calculate the entropy change for a process, we consider the number of moles of the substance involved. This is why the unit of entropy change includes moles in the denominator.

The extensive property of entropy means that the entropy change depends on the quantity of substance involved. For example, the entropy change when 1 mole of a substance is heated will be different from the entropy change when 2 moles of the same substance are heated.

Although entropy is an extensive property per mole, it is useful for comparing the disorderliness of different substances and predicting the spontaneity of processes.