Question

1. For the following compounds and b.p. data, consider the intermolecular forces involved (and review the chapter on intermolecular forces in a first year chemistry textbook if necessary).

methane (CH₄)         b.p. = -164 ⁰C             decane (C₁₀H₂₂)            b.p. = 174 ⁰C

methanol (CH₃OH) b.p. =    65 ⁰C             1-decanol (C₁₀H₂₁OH) b.p. = 229 ⁰C

1. explain why the b.p. of methanol is nearly 230 ⁰C higher than that of methane;

explain why the b.p. of 1-decanol is 55 ⁰C higher than that of decane

2. explain why the difference in b.p. is so much greater between methanol and methane than it is between 1-decanol and decane.

Answer 1

Answer 2

The boiling point of a substance is influenced by the strength of intermolecular forces between its molecules. Different compounds exhibit different intermolecular forces, which can explain the differences in boiling points observed.

1. Methane (CH4) has a boiling point of -164 °C, while methanol (CH3OH) has a boiling point of 65 °C. The significant difference in boiling points can be attributed to the presence of hydrogen bonding in methanol. Methanol molecules can form hydrogen bonds between the oxygen atom of one molecule and the hydrogen atom of another molecule. These hydrogen bonds are stronger than the London dispersion forces present in methane. The presence of hydrogen bonding increases the intermolecular forces in methanol, requiring more energy to break the bonds and reach the boiling point.

2. Decane (C10H22) has a boiling point of 174 °C, while 1-decanol (C10H21OH) has a boiling point of 229 °C. The higher boiling point of 1-decanol compared to decane can be attributed to the presence of hydrogen bonding as well. 1-Decanol contains a hydroxyl group (-OH), which can form hydrogen bonds with other 1-decanol molecules. These hydrogen bonds contribute to stronger intermolecular forces, requiring more energy to break the bonds and reach the boiling point.

3. The difference in boiling points between methanol and methane is significantly greater than the difference between 1-decanol and decane. This is because the intermolecular forces in methanol (hydrogen bonding) are much stronger than in methane (London dispersion forces). The presence of hydrogen bonding in methanol leads to a much higher boiling point compared to methane. On the other hand, although 1-decanol also exhibits hydrogen bonding, the difference in intermolecular forces between 1-decanol