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Ch.11 - Liquids and Intermolecular Forces
Brown - Chemistry: The Central Science 14th Edition
Brown14th EditionChemistry: The Central ScienceISBN: 9780134414232Non è quello che usi tu?Cambia libro di testo
Capitolo 11, Problema 51

(a) Place the following substances in order of increasing volatility: CH4, CBr4, CH2Cl2, CH3Cl, CHBr3, and CH2Br2. (b) How do the boiling points vary through this series? (c) Explain your answer to part (b) in terms of intermolecular forces.

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1
Identify the types of intermolecular forces present in each substance: CH_4, CBr_4, CH_2Cl_2, CH_3Cl, CHBr_3, and CH_2Br_2. Consider London dispersion forces, dipole-dipole interactions, and hydrogen bonding.
Recognize that volatility is inversely related to the strength of intermolecular forces. Substances with weaker intermolecular forces are more volatile.
Arrange the substances in order of increasing volatility by comparing the strength of their intermolecular forces. Consider molecular weight and polarity.
For boiling points, note that they are directly related to the strength of intermolecular forces. Substances with stronger intermolecular forces have higher boiling points.
Explain the variation in boiling points by discussing the role of molecular weight and polarity in determining the strength of London dispersion forces and dipole-dipole interactions.

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Volatility

Volatility refers to the tendency of a substance to vaporize. It is influenced by the strength of intermolecular forces; substances with weaker forces tend to be more volatile. For example, lighter molecules with weaker London dispersion forces will evaporate more readily than heavier molecules with stronger dipole-dipole interactions or hydrogen bonds.
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Boiling Point

The boiling point of a substance is the temperature at which its vapor pressure equals the external pressure, allowing it to transition from liquid to gas. Generally, higher boiling points indicate stronger intermolecular forces. In the context of the given substances, as molecular weight and polarity increase, boiling points typically rise due to enhanced van der Waals forces.
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Boiling Point Elevation

Intermolecular Forces

Intermolecular forces are the forces of attraction or repulsion between molecules. They include London dispersion forces, dipole-dipole interactions, and hydrogen bonds. The type and strength of these forces significantly affect both volatility and boiling points; for instance, substances with stronger intermolecular forces will have lower volatility and higher boiling points compared to those with weaker forces.
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Intermolecular vs Intramolecular Forces