Freezing up liquid in a system then:

Options

A. `q=0`
B. `q gt 0`
C. `q lt 0`
D. `q gt 0` or `q lt 0`

Answer

To solve the question regarding the freezing of a liquid in a system, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Process**: When a liquid freezes, it undergoes a phase change from liquid to solid. This process involves the release of heat energy to the surroundings.

2. **Heat Transfer**: In thermodynamics, the heat transfer (q) during a process can be positive or negative. A positive q indicates heat is absorbed by the system, while a negative q indicates heat is released.

3. **Freezing of Liquid**: During the freezing process, the liquid loses energy in the form of heat to become solid. Therefore, the heat released during this process means that q is negative.

4. **Temperature Change (ΔT)**: The temperature of the system decreases as the liquid freezes. Since the temperature decreases, the change in temperature (ΔT) is also negative.

5. **Relation Between q and ΔT**: The relationship between heat (q), heat capacity (C), and temperature change (ΔT) is given by the equation:
\[ q = C \cdot \Delta T \]
Since we have established that ΔT is negative (due to cooling) and C (heat capacity) is always positive, it follows that q must also be negative.

6. **Conclusion**: Therefore, we conclude that the heat change (q) during the freezing of a liquid is less than zero (q < 0).

### Final Answer:
The correct answer is that q is less than 0.