When thermal energy is added to a system, the temperature of the particles generally increases. This is because temperature is a measure of the average kinetic energy of the particles in a substance. As thermal energy is added, it increases the kinetic energy of the particles, causing them to move more vigorously.
In solids, the particles vibrate more intensely about their fixed positions. In liquids, the particles move more freely and can flow past one another more easily. In gases, the particles gain speed and move more rapidly apart from one another.
However, it's important to note that there are certain circumstances where adding thermal energy may not immediately increase temperature. For example, during a phase change (like melting or boiling), the thermal energy goes into changing the state of the substance rather than increasing its temperature. During such transitions, the temperature remains constant until the phase change is complete.
In summary, adding thermal energy typically raises the temperature of the particles in a substance unless a phase change occurs, which requires energy to be used for breaking intermolecular bonds rather than increasing kinetic energy.