Chemistry glossary Definition of the spontaneous process and examples .In a system, whether in chemistry, biology or physics, there are spontaneous and non-spontaneous processes.
Definition of spontaneous process
A spontaneous process is one that will occur without energy from the environment. It is a process that will happen on its own. For example, a ball will descend a slope, the water will slope, the ice will melt in the water , the radioisotopes will decay and the iron will rust .These reactions occurs in galvanic or electrolytic cells. Redox reactions takes place either spontaneously and produce electricity or it may use electricity to drive non spontaneous reactions.
No interventions are required because these processes are thermodynamically favorable. In other words,we can say that the initial energy is higher than the final energy.
Note how quickly a process occurs does not affect spontaneity or not. It can take a long time for rust to become evident, but when the iron is exposed to air, the process will occur. A radioactive isotope can decay instantly or after thousands, millions, even billions of years.
Spontaneous versus non-spontaneous
Energy must be added for a non-spontaneous process to occur. The reverse of a spontaneous process is a non-spontaneous process. For example, rust does not turn into iron by itself. An isotope girl will not return to her parent state.
Free energy and spontaneity
Gibbs’ free energy change for a process can be used to determine its spontaneity. At constant temperature and pressure, the equation is:
ΔG = ΔH – TΔS
where ΔH is a change in enthalpy and ΔS is a change in entropy.
- If AG is negative, the process is spontaneous.
- If ΔG is positive, the process is non-spontaneous (but spontaneous in the opposite direction).
- If AG is 0 then the process is in equilibrium and no net change occurs over time.
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