A process that occurs without any external intervention is described as what?

• A. Nonspontaneous process
• B. Isothermal process
• C. Endothermic process
• D. Spontaneous process

Answer: (C)

Spontaneity is what determines whether a process can proceed on its own, without ongoing external energy input. A process that occurs without external intervention is spontaneous because it is driven by thermodynamic factors that favor the change under the given conditions. The key criterion is Gibbs free energy: if ΔG is negative at the temperature and pressure of interest, the process proceeds spontaneously; if ΔG is positive, it does not without outside work, and if ΔG is zero, the system is at equilibrium.

Isothermal describes a constant temperature, which is about the condition of the system rather than whether it will self-drive. Endothermic refers to absorbing heat, which is about heat flow direction, not spontaneity itself. A process can be spontaneous and endothermic if the entropy increase is large enough to make ΔG negative. Hence, the best description for a process that happens without external intervention is spontaneous.