Science, Tech, Math › Science Spontaneous Process in Science: Definition and Examples Share Flipboard Email Print A ball rolling down an incline is an example of a spontaneous process. Richard Kolker / Getty Images Science Chemistry Chemical Laws Basics Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated November 27, 2019 In a system, be it chemistry, biology, or physics, there are spontaneous processes and nonspontaneous processes. Definition of a Spontaneous Process A spontaneous process is one that occurs on its own, without any energy input from the outside. For example, a ball will roll down an incline; water will flow downhill; ice will melt into water; radioisotopes will decay; and iron will rust. No intervention is required because these processes are thermodynamically favorable. In other words, the initial energy is higher than the final energy. Note that how quickly a process occurs has no bearing on whether or not it is spontaneous: It may take a long time for rust to become obvious, yet it will develop when iron is exposed to air. A radioactive isotope may decay instantly or after millions or even billions of years; yet, it will decay. Spontaneous Versus Nonspontaneous The reverse of a spontaneous process is a nonspontaneous process: Energy must be added in order for one to occur. For example, rust doesn't convert back into iron on its own; a daughter isotope won't return to its parent state. Gibbs Free Energy and Spontaneity The change in Gibbs free energy or the Gibbs function may be used to assess the spontaneity of a process. At constant temperature and pressure, the Gibbs equation is ΔG = ΔH - TΔS, in which ΔH is the change in enthalpy, ΔS is the change in entropy, and ΔG is the amount of free or available energy. As for the results: If ΔG is negative, the process is spontaneous;If ΔG is positive, the process is nonspontaneous (but would be spontaneous in the reverse direction);If ΔG is zero, then the process is at equilibrium and no net change is occurring over time.