The following compound undergoes a phase transition from the solid to the smectic liquid crystal phase at 121 °C. Upon further heating, the compound undergoes another transition to liquid phase at 131 °C.
(a) Which image represents the arrangement of molecules at 125 °C?

Verified step by step guidance

1. Identify the phase transitions mentioned in the problem: solid to smectic liquid crystal at 121 °C and smectic liquid crystal to liquid at 131 °C.
2. Determine the temperature range for each phase: solid below 121 °C, smectic liquid crystal between 121 °C and 131 °C, and liquid above 131 °C.
3. Recognize that 125 °C falls between 121 °C and 131 °C, indicating the smectic liquid crystal phase.
4. Understand the characteristics of the smectic liquid crystal phase: molecules are arranged in layers with some degree of order within each layer.
5. Conclude that the image representing the arrangement of molecules at 125 °C should show a layered structure typical of the smectic liquid crystal phase.

Key Concepts

Phase Transitions

Phase transitions refer to the changes in the state of matter, such as solid, liquid, and gas, that occur due to variations in temperature or pressure. In this context, the compound transitions from solid to smectic liquid crystal at 121 °C and then to a liquid phase at 131 °C. Understanding these transitions is crucial for predicting molecular arrangements at specific temperatures.

Liquid Crystal Phases

Liquid crystals are substances that exhibit properties between those of conventional liquids and solid crystals. The smectic phase, mentioned in the question, is characterized by layered structures where molecules are arranged in parallel layers, allowing for some fluidity. Recognizing the characteristics of different liquid crystal phases helps in visualizing molecular arrangements at various temperatures.

Molecular Arrangement

Molecular arrangement refers to the specific organization of molecules within a phase. At 125 °C, which is between the smectic and liquid phases, the arrangement will reflect properties of both states. Analyzing the provided image of the liquid phase at 135 °C can help infer the likely arrangement at 125 °C, as the molecules will still exhibit some ordered structure typical of liquid crystals.