boiling points?

Question

Which of the following statements about boiling points of molecular substances are correct ?


a) HF has a higher boiling point than CH4

b) For the boiling points of hydrogen compounds of Group 16
H2Te > H2Se > H2S > H2O

c) For the boiling points of hydrogen compounds of Group 17
HF > HI > HBr > HCl

d) For the boiling points of hydrogen compounds of Group 14
CH4 > SnH4 > GeH4 > SiH4

note, there may be more than one answer

Answer 1

(a). Right. Their molar mass doesn't differ much (Mm(HF) = 20 and Mm(CH4) = 16) but between HF molecules there exists a strong hydrogen bond.

(b) Wrong. Because between H2O molecules there exists hydrogen bond. The right sequence is: H2O> H2Te > H2Se > H2S (because molar mass of H2Te > molar mass H2Se > molar mass H2S)

(c) Right. Between HF molecules hydrogen bond exists and Mm(HI) > Mm(HBr) > Mm(HCl)

(d) Wrong. Here we don't have hydrogen bond and Mm(SnH4) > Mm(GeH4) > Mm(SiH4) > Mm(CH4) so the right answer is: SnH4 > GeH4 > SiH4 > CH4.

Generally, if we don't have hydrogen bonds, the bigger the molar mass of a substance, the higher it's boiling point.

Answer 2

find out which molecule is heavier and which molecule has a hydrogen bond.

b) H2O has a hydrogen bond so its boiling point must be greater than other coumpond listed in part b, even though all the componds have a H molecule in their structure but note that the stong H bond can only happens when H is bounding with O, N or one more substance (i don't remeber).

d) because there is no H bond in any of the molecules, the boiling point increases as the mass of the molecule insreases. so the heaviest molecule has the highest boiling point.

c) is the same as d. (There is no H bond so consider the mass of the molecules)

a) don't know

NOTE: i took chemistry last year and i'm not very sure about my answers. the mey be wrong

Answer 3

Darn, I should know this one! I have a test on this to!
???

Im guessing b and/or d

Am I right?