Spontaneity

A spontaneous process in chemistry is one that happens without the need of external energy. Because spontaneity is unrelated to kinetics or response rate, a spontaneous process might occur swiftly or slowly. The transformation of carbon in the form of a diamond into graphite is a famous example, which may be expressed as follows:

C(s) (diamond)→C(s) (graphite)

This process takes so long that it is undetectable on a human timescale, thus the phrase “diamonds are forever.”

What is Spontaneity?

The total energy in an isolated system remains constant according to the First Law of Thermodynamics. This rule also describes the link between the system’s work and the heat absorbed, without limiting the direction of heat flow.

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

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

Predicting Spontaneity

In general, the total entropy change is the most important metric for describing the spontaneity of any activity. We may claim there is a change in enthalpy and entropy since most chemical reactions are either closed or open systems.

It is claimed that entropy change alone cannot be accountable for the spontaneity of such a process since enthalpy also affects molecular movements, which enhances or lowers randomness. As a result, we utilise the Gibbs energy change to describe a process’ spontaneity.

Gibbs Equation

A state function is Gibbs energy. It is a large piece of land. The following is the general equation for Gibbs energy change at constant temperature:

ΔGsys = ΔHsys – TΔSsys

ΔGsys = Gibbs energy change of the system

ΔHsys = enthalpy change of the system

ΔSsys = entropy change of the system

T = Temperature of the system

For spontaneity, the total entropy change, ΔStotal is always greater than zero.

ΔStotal = ΔSsys + ΔSsurr

ΔStotal= total entropy change for the process

ΔSsys = entropy change of the system

ΔSsurr = entropy change of the surrounding

Equation of Spontaneity

The unexpectedness is something we can foresee. The change in overall entropy of a reaction’s chemistry. The spontaneity of a process is characterised as such. This category encompasses almost every sort of chemical reaction.

Scientists also hypothesised that changes in enthalpy aid in the rise or decrease of chemical reaction unpredictability. The molecular movements are also affected. This is impossible since entropy changes are only conceivable as a result of chance. There are a slew of additional processes awaiting involvement as well.

By studying Gibb’s energy, students may obtain a thorough understanding of spontaneous chemistry and equations.

What is the Spontaneity Process?

The temperature difference between the system and its surroundings is always zero when it is in a thermal equilibrium state.

dT = 0

The shift in enthalpy is to blame. The environment gains the same amount of enthalpy as the system loses it. As a result, scientists have proposed equations that represent the change in entropy for the system as well as the environment.

ΔSsurr=ΔHsurr/T=−ΔHsys/T

ΔSTotal=ΔSsys+(−ΔHsys/T)

ΔHsurr = enthalpy change of the surrounding

ΔHsys = enthalpy change of the system

ΔStotal>0

Entropy change is always more than zero when it is a spontaneity process. So, it is concluded that

TΔSsys – ΔHsys > 0

ΔHsys– TΔSsys < 0

With Gibb’s equation, it is said that ‘ΔGsys< 0’.

Types of Spontaneity

Processes that take place without the need for an initiator

• When you dissolve sugar in water, you get a solution.

• Evaporation is the process of water evaporating from a body of water.

• When nitric oxide and oxygen interact, nitrogen dioxide is produced.

• The reaction between hydrogen and iodine produces hydrogen iodide.

Processes that happen on their own but need to be initiated

• Ignition begins the process of igniting a wax-burning candle.

• The heat causes calcium carbonate to heat up, releasing calcium oxide and carbon dioxide.

• The interaction between hydrogen and oxygen, which led to the production of water, was started by an electric spark. 2H2+O2 = 2H2O

• The interaction between methane and oxygen, which creates carbon dioxide and water, is started by ignition.

Conclusion

If we see any energy change in Gibbs energy of the system as less than zero in a spontaneous chemical reaction, we know it is not a spontaneous process. It may be deduced that the relationship holds true for a spontaneous reaction as well. The system’s enthalpy is negative when it’s an exothermic reaction. As a result, all exothermic reactions are spontaneous. Gibbs’ free energy becomes negative in an endothermic process. It only happens under particular circumstances, such as when the temperature rises or when the entropy change is very large.