Question

In each of the following groups of substances, pick the one that has the given property, respectively:

I. lowest boiling point: HBr, Kr, Br2

II. highest freezing point: H2O, LiBr, HF

III. lowest vapor pressure at 25°C: Cl2, Br2, I2, At2

IV. lowest freezing point: H2, CO, CO2

PLEASE EXPLAIN!!!!

Answer 1

I. lowest boiling point: HBr, Kr, Br2 --> must be the species with lowest intermolecular forces: Br2 = nonpolar Kr = nonpolar, HBr = polar

then between Kr and Br2

Br2 > mass than Kr, therefore lowest BP is Kr

II. highest freezing point: H2O, LiBr, HF --> the species with MOST interactions

from th elist, LiBr --> highest freezing ponit, since it is an ionic salt, has higher interactoins than any other molecular species

III. lowest vapor pressure at 25°C: Cl2, Br2, I2, At2

vapor pressure --> tendecy to become a vapor, therefore, the heavier the species, the lower vapor pressure

from the list, At has the lowest vapor pressure

IV. lowest freezing point: H2, CO, CO2 --> CO is polar, all other are nonpolar. For lowest freezing point, we need the least intermolecular forces

H2 has lowr mass than cO2, therefore, H2 has lowest freezing point