In an isolated system, if the temperature decreases, the entropy of the system generally decreases as well. This relationship is described by the second law of thermodynamics, which states that the entropy of an isolated system tends to increase over time.
Entropy (S) can be thought of as a measure of the system's disorder or the number of possible microscopic configurations that correspond to a given macroscopic state. A decrease in temperature implies a decrease in the average energy of the system's particles, leading to a decrease in their random motion.
When the temperature decreases in an isolated system, several effects can contribute to a decrease in entropy:
Reduced Molecular Disorder: As the temperature decreases, the thermal energy available to the system decreases. Consequently, the molecules or particles comprising the system move more slowly, reducing their overall disorder. This reduction in molecular disorder corresponds to a decrease in entropy.
Solidification or Condensation: In many cases, as temperature decreases, substances transition from the gaseous phase to the liquid or solid phase. During this transition, the particles become more ordered and arrange themselves into specific structures, resulting in a decrease in entropy.
Decreased Number of Microstates: Entropy is closely related to the number of microstates available to a system. Microstates refer to the different arrangements or configurations of the particles at the microscopic level that give rise to the same macroscopic properties. With a decrease in temperature, the system tends to occupy fewer microstates, leading to a decrease in entropy.
It's important to note that while a decrease in temperature generally leads to a decrease in entropy in an isolated system, this relationship is not an absolute rule. There may be exceptions or cases where other factors come into play. However, the overall trend in an isolated system is for entropy to increase over time, and a decrease in temperature typically accompanies a decrease in entropy.