Boiling points forces

Figure 2.5 shows the boiling points of the hydrides in elements of Groups IV. V, VI and VII. Clearly there is an attractive force between the molecules of the hydrides of fluorine, oxygen and nitrogen... 

The dotted lines represent hydrogen bonds. The high boiling point and viscosity of the pure acid indicate strong intermolecular forces of this kind. 

The increases in melting point and boiling point arise because of increased attraction between the free atoms these forces of attraction are van der Waal s forces (p. 47) and they increase with increase of size. These forces are at their weakest between helium atoms, and helium approaches most closely to the ideal gas liquid helium has some notable characteristics, for example it expands on cooling and has very high thermal conductivity. 

Alkanes and cycloalkanes are nonpolar and insoluble m water The forces of attraction between alkane molecules are induced dipole/induced dipole attractive forces The boiling points of alkanes increase as the number of carbon atoms increases Branched alkanes have lower boiling points than their unbranched isomers There is a limit to how closely two molecules can approach each other which is given by the sum of their van der Waals radii... 

Boiling Point When describing the effect of alkane structure on boiling point m Sec tion 2 17 we pointed out that van der Waals attractive forces between neutral molecules are of three types The first two involve induced dipoles and are often referred to as dis persion forces or London forces... 

Because so many factors contribute to the net intermolecular attractive force it is not always possible to predict which of two compounds will have the higher boiling point We can however use the boiling point behavior of selected molecules to inform us of the relative importance of various intermolecular forces and the structural features that influence them... 

Both polar compounds ethanol and fluoroethane have higher boiling points than the nonpolar propane We attribute this to a combination of dipole/mduced dipole and dipole-dipole attractive forces that are present m the liquid states of ethanol and fluo roethane but absent m propane... 

The boiling points of the chlorinated derivatives of methane increase with the num ber of chlorine atoms because of an increase m the induced dipole/mduced dipole attrac tive forces... 

In general aldehydes and ketones have higher boiling points than alkenes because they are more polar and the dipole-dipole attractive forces between molecules are stronger But they have lower boiling points than alcohols because unlike alcohols two carbonyl groups can t form hydrogen bonds to each other... 

The melting points and boiling points of carboxylic acids are higher than those of hydro carbons and oxygen containing organic compounds of comparable size and shape and indicate strong mtermolecular attractive forces... 

Thermodynamic Effects 4.16.2.4.1 Intermolecular forces (i) Melting points and boiling points... 

Vacuum or Pressure The vast majority of all continuous filters use vacuum to provide the driving force for filtration. However, if the feed slurry contains a highly volatile hquid phase, or if it is hot, saturated, and/or near the atmospheric pressure boiling point, the use of pressure for the driving force may be required. Pressure filtration might also be used where the required cake moisture content is lower than that obtainable with vacuum. 

This is a process that takes place via specific chemical forces, and the process is unique to the adsorbent or adsorbate used. In general, it is studied at temperatures much higher than those of the boiling point of the adsorbate consequently, if supported metals are studied, little or no physical adsorption of the chemisorbing gas takes place on the high surface area support. 

Refrigeration, like dilution, reduces the vapor pressure of the material being stored, reducing the driving force (pressure differential) for a leak to the outside environment. If possible, the hazardous material should be cooled to or below its atmospheric pressure boiling point. At this temperature, the rate of flow of a liquid leak will depend only on liquid head or pressure, with no contribution from vapor pressure. The flow through any hole in the vapor space will be small and will be limited to breathing and diffusion. 

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