The boiling points for a set of compounds in a homologous series can be qualitatively predicted using intermolecular force strengths. using their condensed structural formulas, rank the homologous series for a set of alkanes by their boiling point.

rank from highest to lowest boiling point. to rank items as equivalent, overlap them.

a)ch3ch2ch2ch3
b) ch3ch2ch2ch2ch2ch3ch3
c) ch3ch2cch2ch3ch3
d)ch3ch2ch2ch2ch2ch2ch3

Descending order of boiling point: (d)  > (c) > (b) > (a)

Explanation:

The given compounds are:

a) CH₃CH₂CH₂CH₃ – butane (4 carbon Straight-change)

b) CH₃CH₂CH₂CH₂CH₂CH₃ – hexane (6 carbon Straight-change)

c) CH₃CH₂C(CH₃)₂CH₂CH₃ – 3,3-dimethylpentane (7 carbon Branched chain)

d)CH₃CH₂CH₂CH₂CH₂CH₂CH₃ – heptane (7 carbon Straight-change)

Boiling point is defined as the temperature at which the substance changes from the liquid to the vapor state. It is generally dependent upon the molecular mass, branching and the intermolecular forces.

Since all the given compounds are alkanes. Thus, they all exhibit weak intermolecular van der Waals forces.

Therefore, the boiling point of alkanes depends only on the molecular mass or the number of carbon atoms and the branching.

The boiling point of a molecule increases with molecular mass or the number of carbons and decreases with branching.

Therefore, the descending order of boiling point of alkanes is:

(d) CH₃CH₂CH₂CH₂CH₂CH₂CH₃ (heptane, 7 carbon Straight-change) >

(c) CH₃CH₂C(CH₃)₂CH₂CH₃(3,3-dimethylpentane, 7 carbon Branched-chain) >

(b) CH₃CH₂CH₂CH₂CH₂CH₃ (hexane, 6 carbon Straight-change) >

(a) CH₃CH₂CH₂CH₃ (butane, 4 carbon Straight-change)

the ideal gas law equation is as follows

pv = nrt

where p - pressure

v - volume

n - number of moles

r - universal gas constant

t - temperature

so if the pressure, volume and temperature are already known

we are left with n and r

since r is the universal gas constant that has a known fixed value then r too is known

so we are left with 'n'

once we know temperature volume and pressure

we can find the number of moles of gas present using the ideal gas law equation

this is not my own answer, this is an answer for the same question by the user blahblahmali. i do not claim ownership of this account.