Question

please explain ??????????​

Answer 1

Answer:

C should be the correct answer because for spontaneous reaction delta should be negative.

For delta g to be negative t delta s should be greater than delta s

(delta g = delta s- t delta s)

Answer 2

According to the thermodynamics :-

dG° = dH° - TdS°

This is differential equation of GIBBS FREE ENERGY

What is GIBBS FREE ENERGY?

It is the useful energy in a molecule which can be extracted

For example, Your body muscles have energy stored in it but when you are hungry then actually your body needs some energy for performing work either biological works inside the body or physical work which you do.

Then you eat food. Food provides energy for doing work.

But when you are hungry you say you have lost all of your energy but if it's true?

No since your muscles bones and every body parts have energy but that can not be used for satisfying your energy need as that is internal stored energy in your body which can not be extracted but you need energy from outside which is termed as free energy or useful energy.

Similarly molecules are made up of atoms which already contains nucleus and other particles which themselves have energy which is called internal energy and can not be extracted. But in molecules atoms are bonded by several bonds which can be broken and energy can be extracted out from them.

You have feel that when you are tired you don't like to play or move or do works as you feel you have less energy left but when you are full of energy you run here and there with lot of excitement.

Similarly when molecules have more free energy then they are more energetic and therefore less stable. When molecules have less free energy they are more stable.

In nature any system tries to reduce its free energy in order to get stability. No system tries to increase its free energy as it will become unstable.

So any reaction proceeds in forward direction only when the total free energy of products formed is less than that of reactants as it has to become more stable.

So GIBBS FREE ENERGY for products is less than that for reactants

So change in GIBBS FREE ENERGY that is dG° = GIBBS FREE ENERGY for products - GIBBS FREE ENERGY for reactants = -ve < 0

Such type of reactions are called spontaneous reactions.

Negative because GIBBS FREE ENERGY of products is less than that of reactants.

So,

From above equation :-

dG° = dH° - TdS° = - ve

dG° < 0

dH° - TdS° < 0

dH° < TdS°

So third option is correct.

When dG° > 0

Such types of reactions are called non-spontaneous reactions

And when dG° = 0

Such reactions proceed in both directions and are called equilibrium reactions.

Now what will happen if GIBBS FREE ENERGY of products is greater than that of reactants?

Will that reaction not proceed forward?

The answer is no it will not proceed itself. But when you provide energy from outside to the reactants that overall free energy of reactants becomes greater than that of products then in that case reaction can go forward.

NISHANT ABHANGI

(JEE ADVANCED 2019 AIR 6)

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