Standard Gibbs Free Energy Change at Chemical Equilibrium
STATEMENT-1 : For every chemical reaction at equilibrium, standard Gibbs energy of reaction is zero.
and
STATEMENT-2 : At constant temperature and pressure, chemical reactions are spontaneous in the direction of decreasing Gibbs energy.
Options
STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is a correct explanation for STATEMENT-1
STATEMENT-1 is True, STATEMENT-2 is True; STATEMENT-2 is NOT a correct explanation for STATEMENT-1
STATEMENT-1 is True, STATEMENT-2 is False
STATEMENT-1 is False, STATEMENT-2 is True
Topics & Concepts
Step-by-Step Solution
To evaluate the truth value of each statement:
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Analysis of STATEMENT-1:
The relationship between the Gibbs free energy change () and the standard Gibbs free energy change () of a reaction at temperature is given by:
where is the reaction quotient and is the universal gas constant.At chemical equilibrium, the condition for dynamic equilibrium is:
Substituting these values into the thermodynamic relation gives:
The standard Gibbs energy of reaction, , is zero if and only if the equilibrium constant . For an arbitrary reaction at equilibrium, can have any positive value, meaning is generally non-zero.
Therefore, STATEMENT-1 is False. -
Analysis of STATEMENT-2:
According to the Second Law of Thermodynamics, the criterion for spontaneity of a process occurring at constant temperature () and pressure () is given by:
A spontaneous chemical change proceeds in the direction where the total Gibbs energy of the system decreases until it reaches a minimum at equilibrium (where ).
Therefore, STATEMENT-2 is True.
Conclusion:
STATEMENT-1 is False, and STATEMENT-2 is True.
Thus, the correct option is D.