What phenomenon occurs when a material increases in temperature without an external heat source?

Self-heating refers to the process where a material can raise its own temperature due to internal chemical reactions or the breakdown of organic materials, without the need for an external heat source. This phenomenon often occurs in compost piles, oily rags, or certain chemical reactions, where heat is generated internally through exothermic reactions. When the generated heat cannot dissipate quickly enough, the temperature of the material continues to rise, which can potentially lead to ignition if it exceeds the material’s auto-ignition temperature.

In contrast, convection describes the transfer of heat through the movement of fluids, conduction involves the transfer of heat through direct contact between materials, and radiation involves the emission of energy as electromagnetic waves. None of these processes inherently involve a material increasing in temperature due to internal reactions; rather, they focus on heat transfer mechanisms. Hence, self-heating stands out as the correct phenomenon associated with temperature increase without an external heat source.