Iodine has a triple point at \(114^{\circ} \mathrm{C}, 90 \mathrm{~mm} \mathrm{Hg}\). Its critical temperature is \(535^{\circ} \mathrm{C}\). The density of the solid is \(4.93 \mathrm{~g} / \mathrm{cm}^{3}\), and that of the liquid is \(4.00 \mathrm{~g} / \mathrm{cm}^{3}\). Sketch the phase diagram for iodine and use it to fill in the blanks using either "liquid" or "solid." (a) Iodine vapor at \(80 \mathrm{~mm} \mathrm{Hg}\) condenses to the when cooled sufficiently. (b) Iodine vapor at \(125^{\circ} \mathrm{C}\) condenses to the pressure is applied. (c) Iodine vapor at \(700 \mathrm{~mm} \mathrm{Hg}\) condenses to the when cooled above the triple point temperature.

When learning about the phases of matter, one key concept to grasp is the triple point. This is a unique condition where three phases of a substance—solid, liquid, and gas—coexist in equilibrium. It's a singular combination of temperature and pressure at which the transitions between these phases occur simultaneously.

For instance, the triple point of iodine is at 114°C and 90 mm Hg. This means that at this precise condition, iodine can be found as a solid, liquid and gas all at once. If you imagine a phase diagram, which visually represents the different states of matter, the triple point appears as a junction point on the graph where the boundaries between these three phases meet.

In practical scenarios, like in the technical execution of this diagram, you might find it through plotting the known triple point and observing where the phase boundaries intersect. Remember, the triple point is not just a theoretical concept; it has practical implications in fields such as material science and thermodynamics and is crucial for the calibration of thermometers.

Another intriguing aspect of phase diagrams is the presence of a critical temperature. Above this temperature, a substance cannot exist as a liquid, regardless of the applied pressure. It marks the end of the liquid-gas boundary and is an important parameter in understanding the behavior of substances at high temperatures.

For iodine, the critical temperature is a scorching 535°C. When you reach this threshold, iodine's distinct liquid phase disappears, leaving you only with gas—no amount of squeezing (i.e., applying pressure) will condense it back into a liquid. On a phase diagram, you indicate this with a termination point at the high end of the temperature axis—at this point, the liquid and gas phases are indistinguishable, existing as a supercritical fluid.

Recognizing the critical temperature can aid in understanding processes such as the liquefaction of gases and the behavior of natural phenomena, including the atmospheres of large planets and stars, where extremely high temperatures are common.

Phase transitions describe the transformation from one state of matter to another—such as from gas to liquid or liquid to solid—and are intrinsically tied to a substance's phase diagram. The answers to the given exercise hinge on understanding these transitions. They occur across the lines or boundaries on a phase diagram that separate different states of matter.

When conditions such as temperature or pressure change, and a substance crosses these lines, a phase transition occurs. For example, cooling iodine vapor at 80 mm Hg will lead it to condense into a liquid, crossing the gas-liquid boundary. Similarly, increasing the pressure on iodine vapor at 125°C also pushes it over the boundary into a liquid state.

Understanding phase transitions is practical for various applications like refrigeration, where a refrigerant transitions between liquid and gas to absorb and release heat. It's also crucial in manufacturing processes, such as when molten metal solidifies into a particular shape or form.