Question

Interpreting Concepts During the freezing of a substance, energy is being removed from that substance. Yet the temperature of the liquid-solid system remains constant. Explain this phenomenon.

Short answer

Energy removed during freezing is used for phase change, keeping temperature constant due to latent heat of fusion.

Step-by-step solution

Understanding Phase Change

During a phase change, such as freezing, a substance transitions from one state of matter to another. In this case, from liquid to solid.

Energy Removal Explained

Energy is removed from the substance during freezing. This energy removal takes the form of heat leaving the system.

Constant Temperature Explanation

The temperature remains constant because all the removed energy is used to change the phase of the substance, not to lower the temperature. This energy used is known as the latent heat of fusion.

Latent Heat Role

Latent heat is the energy required to change the phase of a substance without changing its temperature. During freezing, the latent heat of fusion is released.

Thermal Equilibrium

The system remains at a thermal equilibrium temperature while the entire liquid is not yet converted to solid.

Key concepts

Latent Heat of Fusion

Latent heat of fusion is a key concept when discussing the phase change during freezing. It refers to the energy needed to change a substance from a liquid to a solid without changing its temperature. This energy is absorbed or released by the substance as it transitions between these states.

For instance, when water freezes, it requires energy removal in the form of heat for the phase change to occur. However, the energy removed does not lower the temperature of the water but instead alters its molecular structure, converting the water into ice. This specific energy involved is termed the latent heat of fusion.

Imagine a scenario where you cool water to its freezing point. Once it reaches 0°C, the temperature halts even though heat continues to leave the system. This is the energy management process entailed in the latent heat of fusion, making sure that phase change happens without a temperature shift.

Temperature Constancy

When a substance undergoes a phase change, such as liquid to solid, it's fascinating to note that its temperature remains constant during the entire process. This phenomenon might seem counterintuitive initially, but it is central to the concept of phase transition.

During freezing, although heat energy is continually being removed, all this energy is directed toward breaking or forming bonds between particles, not toward lowering the substance's temperature. Essentially, the energy is rerouted to facilitate the solidification process rather than changing temperature.

So when you see a liquid-solid system maintaining a steady 0°C while it freezes, this is a direct illustration of temperature constancy. The temperature will not drop further until the phase transition is complete.

Energy Removal

Energy removal is a vital element of the freezing process. With substances undergoing phase changes, energy in the form of heat must be removed to trigger the transformation.

Think about it: when water cools and begins to freeze, what you're observing is the gradual exit of heat energy from the system. This removal happens because the substance needs to lose energy to rearrange its molecular structure—from a less organized liquid state to a more organized solid state.

By consistently removing energy, we ensure that the substance is provided with the necessary conditions to complete the freezing process. This continuous energy extraction happens until all the liquid has transformed into a solid, aligning with the latent heat of fusion concept we discussed earlier.

Thermal Equilibrium

Thermal equilibrium is another crucial idea in understanding the freezing process. This condition occurs when two or more substances interacting reach the same temperature and remain constant.

During a phase change, such as freezing, the system stays in thermal equilibrium. Even as further energy removal happens, the temperature of the liquid-solid system remains stable until the phase transition is fully accomplished.

For example, when water begins to freeze at 0°C, it maintains this temperature throughout the entire freezing duration. The steady temperature indicates that the entire system is in thermal equilibrium. Only when the phase change is complete and all the water has turned to ice will the temperature begin to decrease again, if more heat is extracted.

This balance ensures that the system performs an efficient phase transition from liquid to solid without any instability in temperature, encapsulating the principles of thermal equilibrium.