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.
(b) Which image represents the arrangement of molecules at 135 °C?

Verified step by step guidance

1. Identify the phase transitions described in the problem: solid to smectic liquid crystal at 121 °C, and smectic liquid crystal to liquid at 131 °C.
2. Determine the phase of the compound at 135 °C, which is above the second transition temperature (131 °C).
3. Recognize that at 135 °C, the compound is in the liquid phase.
4. Analyze the provided image to confirm it represents the molecular arrangement in the liquid phase.
5. Conclude that the image shows the arrangement of molecules at 135 °C, which is in the liquid phase.

Key Concepts

Phase Transitions

Phase transitions refer to the changes in the state of matter, such as solid to liquid or liquid to 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 fully liquid phase at 131 °C, illustrating how thermal energy influences molecular arrangement.

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 organized in planes but can flow like a liquid. Understanding these phases is crucial for interpreting the molecular arrangement at different temperatures.

Molecular Arrangement

Molecular arrangement refers to the specific organization of molecules within a substance, which affects its physical properties. At 135 °C, the compound is in a liquid phase, where molecules are more randomly arranged compared to the ordered structure of solids or the layered structure of liquid crystals. Analyzing the image helps identify the correct molecular arrangement at this temperature.