A spontaneous change is one in which the system suffers:
an increase in internal energy
lowering in entropy
lowering in free energy
no energy change

Options

A. an increase in internal energy
B. lowering in entropy
C. lowering in free energy
D. no energy change

Explanation

To solve the question regarding spontaneous changes in a system, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Spontaneity**:
- A spontaneous change refers to a process that occurs without needing to be driven by an external force. In thermodynamics, spontaneity is often assessed using the Gibbs free energy (ΔG).

2. **Recall the Gibbs Free Energy Equation**:
- The Gibbs free energy change (ΔG) is defined as:
\[ ΔG = ΔH - TΔS \]
where ΔH is the change in enthalpy, T is the temperature in Kelvin, and ΔS is the change in entropy.

3. **Identify the Condition for Spontaneity**:
- A reaction is spontaneous when ΔG is negative (ΔG < 0). This indicates that the free energy of the system decreases during the process.

4. **Analyze the Given Options**:
- **Increase in internal energy**: This would imply that the system is gaining energy, which is not indicative of spontaneity.
- **Lowering in entropy**: A decrease in entropy (ΔS < 0) would generally not favor spontaneity unless accompanied by a significant decrease in enthalpy.
- **Lowering in free energy**: This aligns with our understanding that spontaneous processes have a negative ΔG.
- **No energy change**: This does not necessarily indicate spontaneity, as a process can be spontaneous even with energy changes.

5. **Select the Correct Answer**:
- Based on the analysis, the correct answer is that a spontaneous change is one in which the system suffers a **lowering in free energy**.

### Final Answer:
The correct option is: **lowering in free energy**.

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