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Gibbs Energy Change And Criteria For Equilibrium MCQ - Practice Questions with Answers
Edited By admin | Updated on Sep 25, 2023 25:23 PM | #NEET
Quick Facts
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Spontaneity Criteria With Gibbs Energy (G) is considered one the most difficult concept.
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Gibbs Energy And Change In Gibbs Energy is considered one of the most asked concept.
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39 Questions around this concept.
Solve by difficulty
For a particular reversible reaction at temperature were found to be both +Ve.
If is the temperature at equilibrium, the reaction would be spontaneous when
Standard entropy of are 60, 40 and 50 J K-1 mol-1, respectively. For the reaction,
to be at equilibrium, the temperature will be
Match list - 1 (Equations) with list - 2 (Type of processes) and select the correct option
List 1 List 2
Equations Type pf process
(1) (i) Non spontaneous
(2) (ii) Equilibrium
(3) (iii) spontaneous and endothermic
(4) (iv) spontaneous
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In a fuel cell methanol is used as fuel and oxygen gas is used as an oxidizer. The reaction is
At 298 K standard Gibb’s energies of formation for
are –166.2, –237.2 and –394.4 kJ mol-1 respectively. If standard enthalpy of combustion of methanol is –726 kJ mol-1 , efficiency of the fuel cell will be
For the reactions,
$\begin{array}{ll}\mathrm{C}+\mathrm{O}_2 \rightarrow \mathrm{CO}_2 ; & \Delta \mathrm{H}=-393 \mathrm{~J} \\ 2 \mathrm{Zn}+\mathrm{O}_2 \rightarrow 2 \mathrm{ZnO} ; & \Delta H=-412 J\end{array}$
If an endothermic reaction is non-spontaneous at the freezing point of water and becomes feasible at its boiling point, then
The correct thermodynamic conditions for the spontaneous reaction at all temperatures is:
For a given reaction, $\Delta H=35.5 \mathrm{kJmol}^{-1}$ and $\Delta S=83.6 \mathrm{JK}^{-1} \mathrm{~mol}^{-1}$. The reaction is spontaneous at :(Assume that $\Delta H$ and $\Delta S$ do not vary with tempearature)
Which of the following statements is correct for a reversible process in a state of equilibrium?
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and
What will be the magnitude of
at
Concepts Covered - 3
Gibbs Energy And Change In Gibbs Energy
It was introduced in order to relate H, S and to explain spontaneity. According to J. Willard Gibb's Free energy of a system is defined as the maximum amount of energy available to a system during a process that can be converted into useful work.
or
It is the thermodynamic quantity specially characterizing the system, the decrease in whose value during a process is equal to the useful work done by the system.
It is denoted by G and it is given mathematically as follows:
Here,
H = Enthalpy
T = Absolute Temperature
S = Entropy
Also, we learnt that
Therefore, Free energy change at constant temperature and pressure is given as:
At standard condition that is, 298 K and 1 atm pressure
It is called Gibbs equation and it is used to explain criterion of spontaneity, driving force etc.
It is a state function and an extensive property.
Gibb's Free Energy change for a Reaction
For a general reaction, it can be given as follows:
This requires the exact same treatment as or
Gibb's Free Energy Change for small changes in a Reversible process
Now,
Using equations (1) and (2), we can write
Now,
Putting these values in the above expression (3), we have
Note: Remember this important formula for small changes in dG values
Spontaneity Criteria With Gibbs Energy (G)
and Criteria of Spontaneity
Suppose we consider a system which is not isolated from its surroundings then for such a system is given as:
If we consider that qp amount of heat is given by the system to the surroundings at constant temperature and constant pressure then
From equation (i) and (ii)
Or
As according to Gibb-Helmholtz equation,
So,
As for spontaneous process
Hence
Thus for a spontaneous process must be positive.
Or must be negative.
Case I. Suppose both energy and entropy factors oppose a process that is,
Thus, is positive for a non-spontaneous process.
Case II. Suppose both tendencies be equal in magnitude but opposite, that is,
Thus, the process is said to be at equilibrium.
Case III. Suppose entropy and energy, both factors are favourable for a process, that is,
Thus, this process is spontaneous at every temperature.
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Remark |
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+ |
Always -ve |
Spontaneous |
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+ |
- |
Always +ve |
Non-spontaneous |
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+ |
+ |
+ ve at low temp |
Non-spontaneous |
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- ve at high temp |
Spontaneous |
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- ve at low temp |
Spontaneous |
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+ ve at high temp |
Non-spontaneous |
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, Spontaneous process
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, Non-spontaneous process
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, Process in equilibrium
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In exergonic reaction
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In endergonic reaction
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Temperature also play s an important role to decide the spontaneity of a process. A process which is not spontaneous at low temperature can become spontaneous at high temperature and vice-versa.
Gibbs Energy At Equilibrium
Relationship between or
with E or
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Free energy change in an electrochemical cell can be related to electrical work done (E) in cell as follows
when we use standard conditions than
Here = standard E.M.F of the cell
n = No. of moles of e- transferred
F = Faraday's constant
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