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Standard XII
Chemistry
Spontaneity
For a reactio...
Question

For a reaction to be spontaneous, the sign of Gibbs Free Energy change ΔG is ________.

A
always negative
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B
always positive
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C
sometimes negative
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D
sometimes positive
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E
The sign of ΔG has no effect on spontaneity
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Solution

The correct option is A always negative
ΔG= negative for spontaneous reaction.

ΔG= Positive for non-spontaneous reaction.

ΔG= 0 for equilibrium.

Hence, the correct option is A.

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Q. Free energy, G=H−TΔS, is a state function that indicates whether a reaction is spontaneous or non-spontaneous. If you think of TS as the part of the system`s energy that is disordered already, then (H−TS) is the part of the system`s energy that is still ordered and therefore free to cause spontaneous change by becoming disordered.
Also, ΔG=ΔH−TΔS

From the second law of Thermodynamics, a reaction is spontaneous if ΔtotalS is positive, non-spontaneous if ΔtotalS is negative, and at equilibrium if ΔtotalS is zero.

Since, −TΔS=ΔG and since ΔG and ΔS have opposite signs, we can restate the Thermodynamic criterion for the spontaneity of a reaction carried out at a constant temperature and pressure.
If ΔG<0, the reaction is spontaneous
If ΔG>0, the reaction is non-spontaneous
If ΔG=0, the reaction is at equilibrium

Read the above paragraph carefully and answer the following questions based on the above comprehension.

A particular reaction has a negative value for the free energy change. Then at ordinary temperature:

Q. Free energy, G=H−TΔS, is a state function that indicates whether a reaction is spontaneous or non-spontaneous. If you think of TS as the part of the system`s energy that is disordered already, then (H−TS) is the part of the system`s energy that is still ordered and therefore free to cause spontaneous change by becoming disordered.
Also, ΔG=ΔH−TΔS
From the second law of Thermodynamics, a reaction is spontaneous if ΔtotalS is positive, non-spontaneous if ΔtotalS is negative, and at equilibrium if ΔtotalS is zero.
Since, −TΔS=ΔG and since ΔG and ΔS have opposite signs, we can restate the Thermodynamic criterion for the spontaneity of a reaction carried out at a constant temperature and pressure.
If ΔG<0, the reaction is spontaneous
If ΔG>0, the reaction is non-spontaneous
If ΔG=0, the reaction is at equilibrium
Read the above paragraph carefully and answer the following questions based on the above comprehension.
One mol of ice is converted to liquid at 273K; H2O(s) and H2O(l) have entropies 38.20 and 60.03Jmol−1dg−1. Enthalpy change in the conversion will be:

Q. ΔG is the net energy available to do useful work and is a measure of free energy. If a reaction has positive enthalpy change and positive entropy change, under what conditions will the reaction be spontaneous?
Q. A reaction has a enthalpy (ΔH)=−40 kcal at 400 K. Above 400 K, the reaction is spontaneous and below this temperature, it is non spontaneous. The values of Gibbs free energy (ΔG) and entropy (ΔS) at 400 K are respectively:
Q. Free energy, G=H−TΔS, is a state function that indicates whether a reaction is spontaneous or non-spontaneous. If you think of TS as the part of the system`s energy that is disordered already, then (H−TS) is the part of the system`s energy that is still ordered and therefore free to cause spontaneous change by becoming disordered.
Also, ΔG=ΔH−TΔS
From the second law of Thermodynamics, a reaction is spontaneous if ΔtotalS is positive, non-spontaneous if ΔtotalS is negative, and at equilibrium if ΔtotalS is zero.
Since, −TΔS=ΔG and since ΔG and ΔS have opposite signs, we can restate the Thermodynamic criterion for the spontaneity of a reaction carried out at a constant temperature and pressure.
If ΔG<0, the reaction is spontaneous
If ΔG>0, the reaction is non-spontaneous
If ΔG=0, the reaction is at equilibrium
Read the above paragraph carefully and answer the following questions based on the above comprehension.
If an endothermic reaction is non-spontaneous at freezing point of water and becomes feasible at its boiling point, then:

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