Free energy change for a reversible process is

Options

A. `gt0`
B. `lt0`
C. equal to zero
D. unpredictable

Answer

To determine the free energy change (\( \Delta G \)) for a reversible process, we can follow these steps:

### Step 1: Understand the definition of free energy change
The free energy change (\( \Delta G \)) is a thermodynamic quantity that indicates the spontaneity of a process. It is defined as:
\[ \Delta G = \Delta H - T \Delta S \]
where:
- \( \Delta H \) = change in enthalpy
- \( T \) = absolute temperature (in Kelvin)
- \( \Delta S \) = change in entropy

### Step 2: Consider the conditions for a reversible process
For a reversible process occurring at constant temperature and pressure, we can relate the changes in heat and entropy:
- The heat change (\( Q \)) at constant pressure is equal to the change in enthalpy (\( \Delta H \)).
- The heat change for a reversible process is equal to the product of temperature and the change in entropy (\( T \Delta S \)).

### Step 3: Substitute the values into the equation
At constant temperature and pressure, we can express the free energy change as:
\[ \Delta G = Q - Q_{\text{reversible}} \]
For a reversible process, we have \( Q = Q_{\text{reversible}} \). Therefore, substituting this into the equation gives:
\[ \Delta G = Q - Q = 0 \]

### Step 4: Interpret the result
The result \( \Delta G = 0 \) indicates that the system is at equilibrium. In thermodynamics, this means that there is no net change in the system's state, and the process can proceed in either direction without favoring one over the other.

### Conclusion
Thus, the free energy change for a reversible process is:
\[ \Delta G = 0 \]

### Final Answer
The correct option is that the free energy change for a reversible process is **equal to zero**.

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