This comment addresses some points in the paper by de los Santos and López-Lacomba (2013 Eur. J.
Phys. 34 [http://https://doi.org/10.1088/0143-0807/34/3/659] 659 ). More specifically, we clarify
the use of the Clausius relation and argue that the proposed new definition of reversibility is
flawed. Our motivation is the pedagogical need to clarify issues which, despite being subtle, are
perfectly tractable.