Problem 11.34

Name the phase transition in each of the following situations, and indicate whether it is exothermic or endothermic:

(a) Bromine vapor turns to bromine liquid as it is cooled

The process vapor --> liquid is referred to as condensation. Since the phase change is from a less ordered to more ordered state, it is exothermic.

(b) Crystals of iodine disappear from an evaporating dish as they stand in a fume hood.

The transition solid-->vapor is called sublimation. The transition is from a state of more order to a state of less order, and so is endothermic (energy must be input to overcome the intermolecular forces which hold particles in the solid state.)

(c) Rubbing alcohol in an open container slowly disappears

this is evaporation (liq -> vapor); it is endothermic since it represents more order --> less order.

(d) Molten lava from a volcano turns into solid rock.

This is the process liquid --> solid; we refer to this as freezing (or fusion). Since the transition is less order --> more order, it is exothermic.