How do intermolecular forces affect freezing point

A solid with high intermolecular forces will require more energy i. Conversely, as the temperature of a liquid sample decreases, the average kinetic energy of the molecules decreases and they move more slowly. Since the molecules are near each other, the slower they go, the more the intermolecular forces attract them to each other. Molecules with stronger intermolecular forces are pulled together tightly to form a solid at higher temperatures, so their freezing point is higher.

The upper limit of the range is the temperature at which all of the solid phase has transitioned to the liquid phase. Reference guides with accepted values exist in the literature, which are used to identify compounds. One major factor that impacts the melting point of the compound is the type of intermolecular forces that exist within the compound.

Intermolecular forces are either attractive or repulsive between the molecules of a compound. In the solid phase, the molecules of a compound will form an organized lattice structure as the molecules are packed close together.

There are three major types of intermolecular forces:. Each type of intermolecular force has a different strength of attraction. Therefore, compounds containing hydrogen bonds require more energy to break the attraction between molecules than a nonpolar compound that only has London dispersion forces. Thus, the presence of hydrogen bonds increases the melting point of a compound. Reported literature values of melting points assume that you have a pure sample of the compound in question.

Often in the lab or in unknown samples, the samples being tested are not pure compounds. Impurities cause the observed melting point of a mixture to be lower than the actual melting temperature of the pure compound. The observable range is greater than that of the pure substance. In a pure compound, the solid is composed of a uniform and ordered structure and requires a certain amount of temperature to break the structure apart for the compound to transition into the liquid phase. In a mixture containing impurities, the solid phase is composed of a disorganized structure.

This requires much less energy to transition into the liquid phase, thus lowering the melting point. This phenomenon is known as melting point depression. Both HCl and F 2 consist of the same number of atoms and have approximately the same molecular mass. At a temperature of K, molecules of both substances would have the same average KE.

The higher normal boiling point of HCl K compared to F 2 85 K is a reflection of the greater strength of dipole—dipole attractions between HCl molecules, compared to the attractions between nonpolar F 2 molecules. A special type of dipole—dipole force—hydrogen bonds—have a pronounced effect on the properties of condensed phases liquids and solids.

On progressing down the groups, the polarities of the molecules decrease slightly, whereas the sizes of the molecules increase substantially.

The effect of increasingly stronger dispersion forces dominates that of increasingly weaker dipole—dipole attractions, and the boiling points are observed to increase steadily.

Liquids that can be homogeneously mixed in any proportion are said to be miscible. Miscible liquids have similar polarities. On mixing, methanol and water will interact through intermolecular hydrogen bonds and mix; thus, they are miscible.

Likewise, nonpolar liquids like hexane C 6 H 14 and bromine Br 2 are miscible with each other through dispersion forces. Two liquids that do not mix to an appreciable extent are called immiscible.

For example, nonpolar hexane is immiscible in polar water. Relatively weak attractive forces between the hexane and water do not adequately overcome the stronger hydrogen bonding forces between water molecules. This text is adapted from Openstax, Chemistry 2e, Section To learn more about our GDPR policies click here. If you want more info regarding data storage, please contact gdpr jove. Your access has now expired.

Provide feedback to your librarian. If you have any questions, please do not hesitate to reach out to our customer success team. Login processing Chapter Liquids, Solids, and Intermolecular Forces. Chapter 1: Introduction: Matter and Measurement. Chapter 2: Atoms and Elements.

Chapter 3: Molecules, Compounds, and Chemical Equations. Chapter 4: Chemical Quantities and Aqueous Reactions. Chapter 5: Gases. Chapter 6: Thermochemistry. Chapter 7: Electronic Structure of Atoms. Learning Objective Discuss the effects of a solute on the freezing point of a solvent. Key Points The freezing point depression can be calculated using the pure solvent freezing point and the molality of the solution.

At the freezing point, the vapor pressure of both the solid and liquid form of a compound must be equal. The freezing point of a substance is the temperature at which the solid and liquid forms are in equilibrium.

To reattain equilibrium, the freezing point of the solute and solvent mixture is lowered relative to the original pure solvent. Show Sources Boundless vets and curates high-quality, openly licensed content from around the Internet.