Entropy is a measure of disorder or randomness in a system, reflecting the number of possible arrangements of particles. In a closed system, entropy tends to increase over time, indicating a natural progression towards equilibrium. The entropy of a molecule can differ from that of a chemical reaction, as it depends on the specific conditions and interactions involved. While both concepts relate to the distribution of energy and matter, they are not the same; entropy can vary based on the system's constraints. Understanding entropy is crucial for grasping thermodynamic principles and the behavior of systems in different states.