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GIBBS FREE ENERGY AND ENTROPY

In every system there are two types of Energy. They are the Available Energy and the Unavailable Energy.

Here the available energy denotes the energy that the system is free to use for performing work. It is denoted by (G).

The Unavailable Energy is denoted by (T*S), where S is the Entropy of a system. Entropy is the measure of randomness of a system

Therefore total heat content (H) is given by

H = G + T*S eqn (1)

Hence when we measure finite change in heat content we use

DH = DG + T*DS eqn (2)

When any process takes place, some free energy may be used up for that process and so it decreases and hence we find that DG is Negative. Thus we can say that when DG is negative for a process, it will happen on its own or we call it ?spontaneous?

Now when temperature is kept constant and there is no change in the state of matter,

DH = 0 , thus H remains constant hence if for a process, when G decreases, T*S should increase so that H remains constant. Now as T is also constant, only S is variable here, so according to eqn (1), S should increase or by eqn (2), DS should be positive.

Thus in any system, when given a chance, matter tries to exist in a disordered state so that the spontaneous processes take place as arranged by nature. Now to bring these particles of matter in an orderly state, we need to do work or provide energy.

Whenever given a chance, the system tries to go from a state of orderliness to a state of disorderliness perfectly according to the fact that every body in the universe tries to acquire a state of minimum energy and maximum stability, here, orderliness means more energy for the body and disorderliness means less energy, hence the above mentioned behavior.

This tendency is spontaneous and not rehearsed. This is also observed in energy. Even energy exists in spontaneous and non spontaneous states. Out of this, ordered energy can be used to perform work while disordered energy cannot be completely utilized to perform work. An excellent example of disordered energy is heat. And we see that whenever we convert other forms of energy into to heat, the efficiency is almost 100% while the conversion of heat energy into other forms of energy is not even close to that.

Thus finally we can conclude that the energy of a system does exist in two forms, one that is ordered and can be used to perform work and the other form that is in disordered state and cannot be used to perform work. That is why Gibbs called the usable energy of the system as ?Free? energy or the ?energy that is free for use?.

I hope you now have a gist of what free energy and entropy mean

You can answer the following question to test your understanding of this concept

Q..

2 moles of a paramagnetic fluid is taken in a closed vessel placed inside an adiabatic chamber with an electro magnet surrounding it. Keeping the pressure and temperature constant, the magnetic field is switched on and off rapidly. What happens to the entropy of the fluid ?

""THINK HARD"

The answer is:

The Entropy of the system decreases every time the magnetic field is switched on as the particles of the paramagnetic fluid align themselves according to the magnetic field applied. Thus they become orderly and their disorderliness or Entropy decreases.

Thank you for reading this article..

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