Given below are two statements:
Statement I: Physical equilibrium takes place only in closed systems at a given temperature
Statement II: For an equilibrium reaction, $\Delta_r G$ is zero
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Do not confuse $\Delta G$ (which is zero at equilibrium) with $\Delta G^\ominus$ (which is only zero when the equilibrium constant $K = 1$).
At any equilibrium, $\Delta G = 0$ is always true.
Statement I is correct but statement II is not correct
Statement I is not correct but statement II is correct
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The Correct Option isA
Solution and Explanation
Step 1: Understanding the Question:
The question is a conceptual, statement-based problem regarding the physical and thermodynamic conditions of chemical and physical equilibria.
Step 2: Key Formula or Approach:
We must analyze each statement according to the thermodynamic criteria for equilibrium.
Step 3: Detailed Explanation:
• Statement I: "Physical equilibrium takes place only in closed systems at a given temperature."
This statement is correct. Physical equilibria (e.g., solid-liquid, liquid-vapor) can only be sustained in a closed container at a constant temperature.
If the system is open, material will continuously escape (e.g., evaporation of water), preventing the forward and backward rates from becoming equal.
• Statement II: "For an equilibrium reaction, $\Delta_r G$ is zero."
This statement is correct. At constant temperature and pressure, the criterion for dynamic equilibrium is that the change in Gibbs free energy ($\Delta_r G$) must be exactly zero.
This indicates that there is no net driving force for the reaction to proceed in either direction.
• Thus, both Statement I and Statement II are correct.
Step 4: Final Answer:
Both statement I and statement II are correct.
