At 25 °C gallium is a solid with a density of 5.91 g/cm³. Its melting point, 29.8 °C, is low enough that you can melt it by holding it in your hand. 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?

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 for solid, liquid, and gas phases, along with lines that indicate phase transitions. Understanding phase diagrams is crucial for predicting how a substance behaves under different conditions, particularly in terms of melting and boiling points.

Density Anomalies

Density anomalies refer to the unusual behavior of certain substances where their solid form is less dense than their liquid form. For most materials, the solid phase is denser than the liquid phase, but in the case of gallium, the solid has a density of 5.91 g/cm³, while the liquid density is 6.1 g/cm³. This property can lead to unique features in the phase diagram, such as a negative slope in the melting curve.

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 relatively low compared to many metals. The phase transition from solid to liquid in gallium is significant because it can occur at temperatures that are easily achievable, influencing its applications and the shape of its phase diagram.