Victory for the ACT Student Text 15e

304 • S CIENCE

PASSAGE VII

Phase diagrams illustrate the relationship between temperature, pressure, and the phases of matter. Each of the three phases—solid, liquid, and gas—is represented by a section of the phase diagram. The curves represent states of equilibrium between two phases—the substance is present in two phases at once as it passes from one phase to the next. All three phases are present at the triple point. For temperatures and pressures both below the triple point, matter passes directly between the solid and gas phases without passing through the liquid phase. For pressures and temperatures beyond the critical point, the liquid and gas phases converge and become indistinguishable in what is known as a •—’‡”…”‹–‹…ƒŽ ϔŽ—‹† . Supercritical ϐŽ—‹†•…ƒ †‹••‘Ž˜‡ ƒ–‡”‹ƒŽ• Ž‹‡ ƒ Ž‹“—‹† ƒ† ‡ˆˆ—•‡ –Š”‘—‰Š •‘Ž‹†• Ž‹‡ ƒ ‰ƒ•Ǥ ‡›‘† –Š‡…”‹–‹…ƒŽ ’‘‹–ǡ ‘ ƒ‘—– ‘ˆ ’”‡••—”‡ ™‹ŽŽ ”‡•–‘”‡ ƒ •—’‡”…”‹–‹…ƒŽ ϐŽ—‹† –‘ ‹–• Ž‹“—‹† ‘” •‘Ž‹† ’Šƒ•‡ ™‹–Š‘—– decreasing the temperature. Figure 1 shows the phase diagram for water, a liquid at room temperature (21 q C) and atmospheric pressure (1 atm). Figure 2 shows the phase diagram for carbon dioxide, a gas at room temperature and atmospheric pressure.

Figure 1

Figure 2