written 2.8 years ago by |
Phase Diagram : -
A phase diagram is a chart that shows the conditions of pressure and temperature at which distinct phases occur and coexist at equilibrium.
The lines on a phase diagram divide into regions – solid, liquid, and gas.
The phase diagram of sulfur is -
Let's look first at the four areas:
Pink — only rhombic sulfur
Brown — only monoclinic sulfur
Green — only liquid sulfur
Blue — gaseous sulfur
The corresponding curves are:
lower left to ① - the sublimation curve of rhombic S: S(rhombic) ⇌ S(g)
① to② - the sublimation curve of monoclinic S: S(monoclinic) ⇌ S(g)
② to upper right - the vapour pressure curve of liquid S: S(l) ⇌ S(g)
① to ③ - the transition curve for S(rhombic) ⇌ S(monoclinic)
② to ③ - the melting point curve for S(monoclinic) ⇌ S(l)
③ to top - the melting point curve for S(rhombic) ⇌ S(l)
There are three triplets : -
① (95.4 °C, 1 ×$10^{-4}$ atm) - rhombic S is in equilibrium with monoclinic S, and both have the same vapour pressure.
② (119 °C, 5 ×$10^{-4}$ atm) - monoclinic S melts; this is the triple point for $S_m$ ⇌ $S_l$ ⇌ $S_g$
③ (151 °C, 1288 atm) - rhombic, monoclinic, and liquid S are at equilibrium.
The critical point where liquid and gaseous S have the same density is off to the right at 1041 °C and 203.3 atm.