In thermodynamics, entropy is defined as a measure of the randomness or disorder of a system. It quantifies the number of specific ways in which a thermodynamic system can be arranged, reflecting the level of uncertainty or disorder. As a system becomes more disordered, its entropy increases; conversely, as it becomes more ordered, its entropy decreases.
This concept is pivotal in understanding the second law of thermodynamics, which states that in an isolated system, the total entropy can never decrease over time, meaning that processes in such systems naturally tend toward increased disorder. For example, when ice melts into water, the structured arrangement of molecules in the solid state becomes more disordered in the liquid state, resulting in an increase in entropy.
The other options relate to different concepts in thermodynamics. Energy refers to the capacity to do work, temperature is a measure of the average kinetic energy of particles, and heat transfer describes the movement of thermal energy from one object to another. While these concepts are interconnected, they do not encapsulate the definition of entropy, which specifically relates to disorder and randomness in a system.