Spontaneity of a reaction | Non- Spontaneous reaction

Spontaneity does not entail that the reaction happens quickly. Diamond degradation into graphite, for example, is a natural spontaneous process that takes millions of years to complete. The rate of a reaction is determined by the chemical kinetics of the reaction rather than its spontaneity. In a spontaneous process, every reactant has a tendency to generate the matching product. This pattern is linked to stability.

The total energy in an isolated system is always constant, according to the First Law of Thermodynamics. This law also explains the relationship between the system’s work and the heat absorbed, without imposing any restrictions on heat flow direction.

All naturally occurring processes, on the other hand, normally proceed in only one way. What exactly does the term “spontaneity” imply in this context? What are the many factors that influence a spontaneous change’s direction? Let’s see what we can find out!

A spontaneous process is one that cannot be reversed. However, by using some external agents, you can really reverse the process. The quantity of unpredictability in any system is measured by its entropy.

What is Non- Spontaneous Reaction?

A chemical reaction in which the standard change in free energy is positive and energy is absorbed is known as an endergonic reaction (also known as a non-spontaneous reaction or an unfavorable reaction). The overall quantity of energy is a loss (it takes more energy to initiate the reaction than it gives back) therefore the total energy is negative. Endergonic reactions can also be pushed by connecting them through a shared intermediate to a strongly exergonic reaction. Saul Steinberg depicts a non-spontaneous process here.

How to predict the spontaneity of a reaction:

In general, the total entropy change is the most important criterion for determining the spontaneity of any process. We may claim there is a change in enthalpy along with the change in entropy since most chemical processes fall into the closed system and open system categories. Because entropy change affects molecular movements and hence enhances or lowers randomness, entropy change alone cannot account for the spontaneity of such a process. As a result, the Gibbs energy change is used to explain the spontaneity of a process. Gibbs’ energy is a state function with a wide range of applications.

The equation of the Gibbs free energy is described as 

∆G= ∆H – T∆S

The Process of Spontaneity:

• The Gibbs equation allows us to predict reaction spontaneity directly from enthalpy and entropy measurements. 

• When a reaction is exothermic, the system’s enthalpy is negative, resulting in a negative Gibbs free energy. As a result, all exothermic reactions are considered spontaneous.

• When the enthalpy of the system is positive, endothermic reactions occur spontaneously under two conditions:

• The temperature is extremely high, causing the Gibbs energy value to be negative.

• To make the Gibbs free energy negative, the entropy shift must be quite high.
• Spontaneity can only indicate whether a reaction can occur, whether it will. 

• At Standard Temperature and Pressure (STP), for example, the spontaneous conversion of diamond to graphite occurs, but it is a gradual process. The makeover will take years to complete.

Spontaneous Process:

• A spontaneous process is one that occurs naturally in a system and does not require intervention from outside the system (an outside agency) to continue.

• A good example of a spontaneous process is the cooling down of heated water.
• The rusting of iron is a reverse process, it always proceeds in the same direction and is a natural occurrence.

2 Fe2 O3 (s) → 4 Fe (s) + 3 O2 (g) 

Non- Spontaneous Process:

• Non-Spontaneous Process is a term that refers to a process that does not happen spontaneously. A non-spontaneous process will not occur unless some external action is done on a regular basis.
• A non-spontaneous process is the heating of water (at room temperature).
• The rusting of iron is a non-spontaneous process.

The Difference Between Spontaneous and Non-Spontaneous Processes

A spontaneous process takes place when certain circumstances are met. A non-spontaneous process, on the other hand, will not occur unless it is “driven” by a constant supply of energy from outside. On the contrary, a process that is spontaneous in one direction under a specific set of parameters is non-spontaneous. Ice melts spontaneously at ambient temperature and normal air pressure, while water does not.

• The reversal process is non Spontaneous if a process is spontaneous.

• All spontaneous processes, as well as the majority of non-spontaneous processes, are feasible.

Non-spontaneous processes require the assistance of an outside entity to occur, whereas spontaneous processes occur naturally.

The term “spontaneous process” refers to a process that, under certain conditions, can occur on its own or by initiation independent of the rate.

The term “spontaneous process” refers to a process that can occur on its own or has a strong desire or proclivity to occur.

A viable process is simply referred to as a spontaneous process.

The speed of the process might range from very sluggish to quick.

Here are some examples of self-contained processes:

1) Water dissipation of common salt

2) When water is evaporated in an open pot

3) Heat transfers from a hot end to a cold end, or a hot body to a cold body.

4) Water flowing down a hill

5) Nitrogen dioxide is formed by combining nitric oxide and oxygen.

2 NO (g) + O2 (g) = 2 NO2 (g)

Conclusion

Under some situations, chemical and physical processes have a natural tendency to go in one direction. A spontaneous process does not require a constant supply of energy from an external source, whereas a non-spontaneous process does. Systems that go through a spontaneous process may or may not acquire or lose energy, but they will see a shift in how matter and/or energy are distributed within the system.