Figure 1. Transitions between solid, liquid, and gaseous states of a substance occur when conditions of temperature or pressure favor the associated changes in intermolecular forces. (Note: The space between particles in the gas phase is much greater than shown.) Source: OpenStax Chemistry 2e
OpenStax Chemistry 2e
The differences in the properties of a solid, liquid, or gas reflect the strengths of the attractive forces between the atoms, molecules, or ions that make up each phase. The phase in which a substance exists depends on the relative extents of its intermolecular forces (IMFs) and the kinetic energies (KE) of its molecules. IMFs are the various forces of attraction that may exist between the atoms and molecules of a substance due to electrostatic phenomena, as will be detailed in this module. These forces serve to hold particles close together, whereas the particles’ KE provides the energy required to overcome the attractive forces and thus increase the distance between particles. Figure 1 illustrates how changes in physical state may be induced by changing the temperature, hence, the average KE, of a given substance.
As an example of the processes depicted in this figure, consider a sample of water. When gaseous water is cooled sufficiently, the attractions between H2O molecules will be capable of holding them together when they come into contact with each other; the gas condenses, forming liquid H2O. For example, liquid water forms on the outside of a cold glass as the water vapor in the air is cooled by the cold glass, as seen in Figure 2.
We can also liquefy many gases by compressing them, if the temperature is not too high. The increased pressure brings the molecules of a gas closer together, such that the attractions between the molecules become strong relative to their KE. Consequently, they form liquids. Butane, C4H10, is the fuel used in disposable lighters and is a gas at standard temperature and pressure. Inside the lighter’s fuel compartment, the butane is compressed to a pressure that results in its condensation to the liquid state, as shown in Figure 3.
Finally, if the temperature of a liquid becomes sufficiently low, or the pressure on the liquid becomes sufficiently high, the molecules of the liquid no longer have enough KE to overcome the IMF between them, and a solid forms.
Flowers, P., Theopold, K., Langley, R., & Robinson, W. R. (2019, February 14). Chemistry 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/books/chemistry-2e
Research Article: An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics
Date Published: August 01, 2016 Publisher: International Union of Crystallography Author(s): Edward O. Pyzer-Knapp, Hugh P. G. Thompson, Graeme M. Day. http://doi.org/10.1107/S2052520616007708 Abstract: An empirically parameterized intermolecular force field is developed for crystal structure modelling and prediction. The model is optimized for use with an atomic multipole description of electrostatic interactions. Partial Text The role … Continue reading
Research Article: Preventing Disulfide Bond Formation Weakens Non-Covalent Forces among Lysozyme Aggregates
Date Published: February 14, 2014 Publisher: Public Library of Science Author(s): Vijay Kumar Ravi, Mohit Goel, Hema Chandra Kotamarthi, Sri Rama Koti Ainavarapu, Rajaram Swaminathan, Etienne Dague. http://doi.org/10.1371/journal.pone.0087012 Abstract: Nonnative disulfide bonds have been observed among protein aggregates in several diseases like amyotrophic lateral sclerosis, cataract and so on. The molecular mechanism by which formation … Continue reading
Date Published: December 29, 2014 Publisher: Public Library of Science Author(s): Daniela Aschenbrenner, Diana A. Pippig, Kamila Klamecka, Katja Limmer, Heinrich Leonhardt, Hermann E. Gaub, Gideon Schreiber. http://doi.org/10.1371/journal.pone.0115049 Abstract: Quantitative proteome research is greatly promoted by high-resolution parallel format assays. A characterization of protein complexes based on binding forces offers an unparalleled dynamic range and … Continue reading
Research Article: Re-refinement from deposited X-ray data can deliver improved models for most PDB entries
Date Published: February 01, 2009 Publisher: International Union of Crystallography Author(s): Robbie P. Joosten, Thomas Womack, Gert Vriend, Gérard Bricogne. http://doi.org/10.1107/S0907444908037591 Abstract: An evaluation of validation and real-space intervention possibilities for improving existing automated (re-)refinement methods. Partial Text The availability of three-dimensional macromolecular coordinates is a prerequisite for many types of studies, such as engineering … Continue reading