What does it mean when a material undergoes thermal decomposition?

When a material undergoes thermal decomposition, it experiences a chemical change where it breaks down into simpler components when subjected to heat. This process is often irreversible, meaning that the original material cannot be regained simply by removing the heat. For example, when wood is heated, it can decompose into charcoal, water vapor, and various gases, fundamentally altering its chemical structure.

While other options discuss various changes that materials might undergo, they do not capture the essential characteristic of thermal decomposition. For instance, maintaining chemical structure would contradict the very nature of thermal decomposition, as it involves breaking down that structure. Changes from solid to gas can happen through processes like sublimation but are not indicative of decomposition. Likewise, evaporation refers specifically to the process of a liquid turning into gas, which is distinct from what happens during thermal decomposition.