Chemistry Homework: Comparing Boiling Points and Intermolecular Forces

This chemistry assignment analyzes the boiling points of 1-pentanol and 2-pentanone, focusing on the influence of intermolecular forces. The introduction defines boiling point and highlights the factors affecting it, including branching, carbon chain length, and intermolecular forces. The assignment compares the boiling points of the two compounds, explaining that 1-pentanol has a higher boiling point due to the presence of hydrogen bonding, dipole-dipole interactions, and London dispersion forces, making its intermolecular forces stronger. The assignment contrasts this with 2-pentanone, which lacks hydrogen bonding, and therefore has weaker intermolecular forces. The conclusion reiterates that the strong intermolecular forces in 1-pentanol require more energy to break, resulting in a higher boiling point. The document includes references to relevant chemistry resources.

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Introduction
Boiling point is the minimum temperature of any substance at which the liquid phase of the
substance turns into gaseous phase. Boiling point is considered to be an imperative aspect in
order to measure the strength of forces present between the molecules (Stone, 2013).
The three main aspects which affect the boiling point of any substance are as highlighted below
(Ashenhurs, 2011):
 Presence of branching in substance reduces the boiling point
 High number of carbon molecules increases the boiling point
 Strength of intermolecular forces
(Hydrogen bonding > Dipole−dipole force> Londondispersion force)
Intermolecular forces are the forces which are working between the molecules of the compound
and bind them together. These forces are London dispersion, hydrogen bonding and dipole-
dipole force and so forth.
The boiling point of 1-pentanol and 2- pentanone are as given below (Kelter, Mosher and Scott,
2008):
Compound Chemical Formula Boiling Point Inter molecule forces
1-pentanol C5H12O 138 oC  Hydrogen bonding
 Dipole-dipole
interaction
 London dispersion
interaction
2- pentanone C5H10 O 101 oC  Dipole-dipole
interaction
 London dispersion
interaction
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London dispersion force is considered to be the weakest intermolecular force. It is termed as
temporary attractive force. This force is acting between both types of molecules i.e. polar and
non-polar. The shape and size of the molecular are pivotal aspects of this force. Small size and
heavier atoms exhibit strong dispersion force. The shape of atom’s molecule affects the
dispersion force’s magnitude for the atom (Clungston and Flemming, 2000).
Presence of hydrogen atom connected covalently with carbon or other atom would result
hydrogen bonding in the molecule. This strongly binds the molecules and increases the boiling
point of substance.
It is apparent from the figures that boiling point of 1-pentanol is higher than boiling point of 2-
pentanone. The main reason of higher boiling point of 1-pentanol is presence of strong
intermolecular force between the molecules. Molecules of 1-pentanol are strongly binding with
each other due to high intermolecular forces which are acting between them. Therefore, their
molecules require high amount of energy in order react with other molecules. Hence, high
temperature is required to break these intermolecular forces and as a result, 1-pentanol shows
high boiling points (Stone, 2013).
Conclusion
The boiling point 1- pentanol is higher than 2-pentanonn of due to presence of strong
intermolecular forces between the molecules. In this case, 1-pentanol presence of strong
functional group (i.e. –OH) results hydrogen bonding and also have London and dipole –dipole
intermolecular force and therefore, the molecules of 1- pentanol required more energy in regards
to react with molecules or to convert into gaseous phase. On the other hand, molecules of 1-
pentanone does not have hydrogen boding and hence, the molecules are binding with weaker
forces. Therefore, 1-pentanol is showing high boiling point as compared with 2- pentanone.
Reference
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Ashenhurs, J. (2011). Three Trends That Affect Boiling Points [Online]. Available at:
http://www.masterorganicchemistry.com/2010/10/25/3-trends-that-affect-boiling-points/
[Accessed 2012].
Clungston, M. and Flemming, R. (2000). Advanced Chemistry. 4th edn. Oxford: OUP Oxford
University Press.
Kelter, B.P., Mosher, D. M., and Scott, A. (2008).Chemistry: The Practical Science. 10th edn.
Sydney: Cengage Leaning Publication.
Stone, A. (2013). The Theory of Intermolecular forces. 2nd edn. Oxford: Oxford University
Press.
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