Textbook Question
In each pair of compounds, pick the one with the higher boiling point. Explain your reasoning. a. CH3OH or CH3SH b. CH3OCH3 or CH3CH2OH
Ch.11 - Liquids, Solids & Intermolecular Forces
Chapter 11, Problem 42b
In each pair of compounds, pick the one with the higher boiling point. Explain your reasoning. b. CS2 or CO2
Verified step by step guidance1
Identify the type of intermolecular forces present in each compound. CS_2 and CO_2 are both nonpolar molecules, so they primarily exhibit London dispersion forces.
Consider the molecular weights of the compounds. CS_2 has a higher molecular weight than CO_2, which generally leads to stronger London dispersion forces.
Analyze the molecular shape and symmetry. CO_2 is a linear molecule, while CS_2 is also linear, but the larger size of sulfur compared to oxygen can affect the strength of dispersion forces.
Evaluate the polarizability of the molecules. Larger atoms like sulfur in CS_2 are more polarizable than smaller atoms like oxygen in CO_2, leading to stronger dispersion forces in CS_2.
Conclude that the compound with stronger intermolecular forces will have a higher boiling point. Since CS_2 has stronger London dispersion forces due to its higher molecular weight and greater polarizability, it will have a higher boiling point than CO_2.
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Key Concepts
Here are the essential concepts you must grasp in order to answer the question correctly.
Intermolecular Forces
Intermolecular forces are the attractive forces between molecules that influence physical properties like boiling points. The main types include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. Stronger intermolecular forces typically result in higher boiling points, as more energy is required to separate the molecules.
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Molecular Structure and Polarity
The molecular structure and polarity of a compound significantly affect its boiling point. Polar molecules, which have a positive and negative end due to uneven electron distribution, generally exhibit stronger dipole-dipole interactions compared to nonpolar molecules. This polarity can lead to higher boiling points in polar compounds compared to their nonpolar counterparts.
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Molar Mass
Molar mass can influence boiling points, particularly in nonpolar molecules where London dispersion forces are the primary intermolecular force. Generally, larger molecules with greater molar mass have stronger dispersion forces due to increased electron cloud size, which can lead to higher boiling points. However, this effect is often secondary to the influence of polarity and intermolecular forces.
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