When most elastomeric polymers (e.g., a rubber band) are stretched, the molecules become more ordered, as illustrated here:
Suppose you stretch a rubber band. (a) Do you expect the entropy of the system to increase or decrease?

Key Concepts

Entropy

Entropy is a measure of the disorder or randomness in a system. In thermodynamics, it quantifies the number of possible arrangements of particles in a system. A higher entropy indicates a more disordered state, while lower entropy suggests a more ordered state. Understanding how entropy changes during physical processes is crucial for predicting the behavior of materials, such as elastomers.

Molecular Order in Polymers

Polymers, like rubber, consist of long chains of repeating units. When stretched, the molecular chains align more closely, leading to increased order within the material. This alignment reduces the freedom of movement of the polymer chains, which can affect the overall entropy of the system. Recognizing how stretching influences molecular arrangement is key to understanding the thermodynamic properties of elastomers.

Thermodynamic Principles

Thermodynamic principles govern the behavior of energy and matter in systems. The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time. When analyzing the stretching of a rubber band, it is essential to consider how energy input (stretching) affects the system's entropy and whether the overall process leads to an increase or decrease in entropy.