Question:
For a spontaneous process at constant temperature and pressure, the change in Gibbs free energy ($\Delta G$) is
For a spontaneous process at constant temperature and pressure, the change in Gibbs free energy ($\Delta G$) is
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Remember that for any spontaneous process under standard conditions of constant temperature and pressure, $\Delta G < 0$.
Updated On: Jun 3, 2026
- Negative
- Positive
- Zero
- Infinite
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The Correct Option is A
Solution and Explanation
Step 1: Concept
Gibbs free energy ($\Delta G$) is a thermodynamic potential that measures the maximum reversible work done by a system at constant temperature and pressure. A spontaneous process occurs when $\Delta G < 0$, indicating that the system can do useful work.
Step 2: Meaning
For a process to be spontaneous under standard conditions of constant temperature and pressure, the change in Gibbs free energy must be negative. This means that the system releases more energy than it requires for the process to occur, allowing it to proceed without an external input of energy.
Step 3: Analysis
To understand why $\Delta G$ is negative for a spontaneous process, consider the definition of Gibbs free energy: \[\Delta G = \Delta H - T\Delta S\] where $\Delta H$ is the change in enthalpy and $T\Delta S$ is the product of temperature and the change in entropy. For a process to be spontaneous at constant temperature and pressure, both conditions must be met: 1. The system must release energy (exothermic) or have a decrease in enthalpy ($\Delta H < 0$). 2. The increase in entropy ($\Delta S > 0$) must be sufficient to make the term $T\Delta S$ positive and large enough to offset any positive $\Delta H$, ensuring that $\Delta G < 0$.
Step 4: Conclusion
Since a spontaneous process at constant temperature and pressure requires that the system can do work, it follows that $\Delta G$ must be negative. This ensures that the energy available for doing useful work is greater than zero.
Final Answer: (A)
Gibbs free energy ($\Delta G$) is a thermodynamic potential that measures the maximum reversible work done by a system at constant temperature and pressure. A spontaneous process occurs when $\Delta G < 0$, indicating that the system can do useful work.
Step 2: Meaning
For a process to be spontaneous under standard conditions of constant temperature and pressure, the change in Gibbs free energy must be negative. This means that the system releases more energy than it requires for the process to occur, allowing it to proceed without an external input of energy.
Step 3: Analysis
To understand why $\Delta G$ is negative for a spontaneous process, consider the definition of Gibbs free energy: \[\Delta G = \Delta H - T\Delta S\] where $\Delta H$ is the change in enthalpy and $T\Delta S$ is the product of temperature and the change in entropy. For a process to be spontaneous at constant temperature and pressure, both conditions must be met: 1. The system must release energy (exothermic) or have a decrease in enthalpy ($\Delta H < 0$). 2. The increase in entropy ($\Delta S > 0$) must be sufficient to make the term $T\Delta S$ positive and large enough to offset any positive $\Delta H$, ensuring that $\Delta G < 0$.
Step 4: Conclusion
Since a spontaneous process at constant temperature and pressure requires that the system can do work, it follows that $\Delta G$ must be negative. This ensures that the energy available for doing useful work is greater than zero.
Final Answer: (A)
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