What does the term "thermal energy" signify?

Thermal energy refers to the total kinetic energy of the particles within a substance, which includes the energy due to the motion of both the individual particles and their vibrations. This kinetic energy is directly related to temperature; as the temperature of a substance increases, the thermal energy increases because the particles move more rapidly. This concept is fundamental in understanding heat transfer and the behavior of matter in different states.

The other options focus on different forms of energy. The first option discusses chemical bond energy, which pertains to the potential energy associated with the arrangement of atoms in a molecule rather than their motion. The second option describes the energy needed for a phase change, such as from solid to gas, highlighting a specific process rather than the overall kinetic energy of particles. The last option confines the definition to energy in chemical reactions, while thermal energy encompasses the broader concept of particle motion, regardless of whether a reaction is occurring. Thus, focusing on the total kinetic energy provides the most accurate and comprehensive understanding of thermal energy.