At 25°C gallium is a solid with a density of 5.91 g/cm³ and a melting point, 29.8°C, just slightly above room temperature. The density of liquid gallium just above the melting point is 6.1 g/cm³. Based on this information, what unusual feature would you expect to find in the phase diagram of gallium?

Verified step by step guidance

1. Step 1: Understand the problem. The problem provides information about the density of gallium in its solid and liquid states. The density of solid gallium is less than the density of liquid gallium.
2. Step 2: Recall the general trend in phase diagrams. Typically, the solid phase of a substance is denser than its liquid phase. This is why, for most substances, the solid phase sinks in the liquid phase.
3. Step 3: Identify the unusual feature. Given that the density of solid gallium is less than the density of liquid gallium, we can infer that solid gallium would float in liquid gallium. This is an unusual feature.
4. Step 4: Reflect this feature in the phase diagram. In a typical phase diagram, the line between the solid and liquid phases slopes to the right with increasing pressure. However, for substances like gallium where the solid is less dense than the liquid, this line would slope to the left. This is because increasing pressure would favor the phase with higher density, which is the liquid phase in this case.
5. Step 5: Conclude the solution. Therefore, the unusual feature you would expect to find in the phase diagram of gallium is that the line between the solid and liquid phases slopes to the left, indicating that the solid phase is less dense than the liquid phase.

Key Concepts

Phase Diagrams

A phase diagram is a graphical representation that shows the phases of a substance at various temperatures and pressures. It typically includes regions where the substance exists as a solid, liquid, or gas, and lines that indicate phase transitions. Understanding phase diagrams is crucial for predicting how a substance behaves under different conditions.

Density Anomalies in Phase Changes

Most substances become denser as they transition from liquid to solid; however, gallium exhibits an unusual behavior where its solid form is less dense than its liquid form. This anomaly can lead to the solid phase floating on the liquid phase, which is contrary to the typical behavior of most materials. Recognizing this property is essential for interpreting gallium's phase diagram.

Melting Point and Phase Transition

The melting point is the temperature at which a solid becomes a liquid, marking a phase transition. For gallium, this occurs at 29.8°C, which is just above room temperature. This low melting point indicates that gallium can exist in both solid and liquid states at relatively mild temperatures, influencing its phase diagram and the behavior of its phases.