File Name: intermolecular forces on boilig point and solubility .zip
Properties like melting and boiling points are a measure of how strong the attractive forces are between individual atoms or molecules. It all flows from this general principle: as bonds become more polarized, the charges on the atoms become greater, which leads to greater intermolecular attractions, which leads to higher boiling points. Now available — Download this awesome free 3-page handout on how to solve common boiling point problems.
Part 1. Sub-index for this page. Natural gas is mainly methane CH 4 , but crude oil contains a wide range of hydrocarbons and other compounds too. The products from crude oil are separated by fractional distillation.
You should appreciate how the uses of the fractions is often related to its molecular size and hence the intermolecular forces intermolecular bonding e. See other notes for Isomerism of alkanes and the effect on boiling point. Other sources of alkanes. Another possible source of methane is called 'methane hydrate' also known as 'methane clathrate' and is believed to be the world's largest reserve of natural gas..
It consists of methane gas trapped in an ice cage of hydrogen bonded water molecules, which is why it is sometimes incorrectly called 'methane ice'. Their formation of CH 4. It has a clearly defined regular crystal structure, but it is not a real compound, because there are no chemical bonds between the methane and water.
All the molecules are held in place by intermolecular forces: transient dipole H 2 O interactions and hydrogen bonding for H 2 O H 2 O interactions - hope you find this little diversion interesting!
There are other structures known with a different ratio of components and with other trapped-caged gases too. Huge amounts of methane hydrate have been found under Arctic permafrost, beneath Antarctic ice, and also in sedimentary deposits along continental margins. Some are close to high-population areas than any natural gas field may allow countries that currently import natural gas to become self-sufficient.
Though it is some task to find safe, economical ways to develop methane hydrate. The methane gas has been formed over thousands of years from the action of anaerobic acting organisms that metabolise organic detritus material.
We are trying to reduce our dependency on fossil fuels, to minimise carbon dioxide emissions, to reduce the greenhouse effect and minimise global warming, so why produce even more. Methane is a very powerful greenhouse gas and is beginning to leak out as the oceans and arctic regions are warming up - exploitation of this reserve cannot help matters e. There is also concern about methane leaking from disused oil and gas wells e. Canada as , wells that may present a 'greenhouse' hazard situation.
The graphs below, only consider the series of linear alkanes from CH 4 to C 14 H Space filling diagrams to illustrate the different magnitudes of the intermolecular bonding forces between two alkanes of different molecular sizes different number of carbon atoms, different numbers of electrons. This gives rise to octane having a boiling point of o C and octadecane a boiling point of o C.
In the above diagram the alkane molecules have been drawn in a linear manner and they would be described as linear alkanes because there are no branches in the carbon chain. However, as illustrated in the 2nd diagram below, they are flexible from propane onwards and even the two methyl groups of ethane can freely rotate with respect to each other! Note: The red line represents linear alkanes in all the graphs A plot of number of electrons in an alkane molecule versus its boiling point K shows a steady rise with a gradually decreasing gradient.
Graph 1 is probably the best graph to look at the relative effects on intermolecular forces intermolecular bonding on boiling point because it is the distortion of the electron clouds e. A plot of the molecular mass of an alkane molecule versus its boiling point K shows a steady rise with a gradually decreasing gradient. A plot of number of carbon atoms in an alkane molecule versus its boiling point K shows a steady rise with a gradually decreasing gradient. The values of these ' latent heats ' are primarily determined by the generally weak but not always!
As the length of the carbon chain increases for linear alkanes, the energy required for vaporisation steadily increases. Therefore to vaporise a molecule, the larger it is, the greater the volume of electron clouds to distort, the greater the kinetic energy required to overcome the intermolecular bonding forces of the instantaneous dipole — induced dipole attractions - see the graph below showing the expected trend and pictorially in the diagram above.
This begs the question, at what point does the enthalpy of vapourisation exceed the C-C bond enthalpy? The highest boiling point I could find on the internet was for C 43 H 88 bpt is o C. This sort of data is important when considering the high temperature thermal degradation and combustion incineration of large hydrocarbon alkane molecules and poly alkene polymers e.
See also The thermal stability of poly alkene plastics. The scenario described above suggests that it might be impossible to distil high boiling compounds without simultaneous thermal decomposition at atmospheric pressure.
Not so, t here are two ways of distilling high boiling compounds to avoid thermal decomposition. The vapour pressure exerted by a liquid rises, exponentially, with increase in temperature. A liquid boils when the vapour pressure it exerts, equals the ambient pressure e.
Therefore, whenever you reduce the pressure above a liquid, it will boil at a lower temperature and this can be low enough to avoid thermal decomposition.
For more details see Vapour pressure and boiling point of a liquid. You pass steam through the mixture containing the substance you want to extract. However, you do have to separate the desired product from the condensed steam distillate. For more details see Steam distillation — theory, practice and uses. The non-polar alkane molecules cannot hydrogen bond with water. Neither are the weak hydrocarbon - water interactions strong enough to disrupt the strong hydrogen bonding between water molecules.
Alkanes, gases, liquids or solids, will dissolve in non-polar solvents like hexane or tetrachloromethane, where the solute-solute, solute-solvent and solvent-solvent intermolecular forces are of a similar magnitude and the dissolving process does not involve breaking strong intermolecular boding..
Doc Brown's Chemistry. Enter chemistry words e. Sub-index for this page 1 Sources of alkanes and the fractional distillation of crude oil 2 The boiling point trend of alkanes and intermolecular forces 3 The trend in enthalpy of vaporisation 4 The solubility of alkanes [ SEARCH BOX ]. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted.
Most of the common alcohols are colourless liquids at room temperature. Methyl alcohol, ethyl alcohol, and isopropyl alcohol are free-flowing liquids with fruity odours. The higher alcohols—those containing 4 to 10 carbon atoms—are somewhat viscous, or oily, and they have heavier fruity odours. Some of the highly branched alcohols and many alcohols containing more than 12 carbon atoms are solids at room temperature. The boiling points of alcohols are much higher than those of alkanes with similar molecular weights. Such a large difference in boiling points indicates that molecules of ethanol are attracted to one another much more strongly than are propane molecules.
On this page you can read or download investigating the effects of intermolecular forces on boiling points in PDF format. The stronger the IMFs, the lower the vapor pressure of the substance and the higher the boiling point. Intermolecular forces determine bulk properties such as the melting points of solids and the boiling points of liquids. Other groups beside hydrogen can be involved in polar covalent bonding with strongly electronegative atoms. Chapter 11 —focus points: Intermolecular forces and their effect on properties of liquids Intermolecular or interparticle forces are weak interactions between particles.
Part 1. Sub-index for this page. Natural gas is mainly methane CH 4 , but crude oil contains a wide range of hydrocarbons and other compounds too. The products from crude oil are separated by fractional distillation. You should appreciate how the uses of the fractions is often related to its molecular size and hence the intermolecular forces intermolecular bonding e.
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In introductory chemistry courses students are presented with the model that matter is composed of particles, and that weak forces of attraction exist between them. This model is used to interpret phenomena such as solubility and melting points, and aids in understanding the changes in states of matter as opposed to chemical reactions. Written tests were administered to students in grades 11 to 13 aged 16 to 19 in Germany. Results indicate students had difficulty predicting the relative boiling points of organic compounds.
Intermolecular forces IMFs can be used to predict relative boiling points. The stronger the IMFs, the lower the vapor pressure of the substance and the higher the boiling point. Therefore, we can compare the relative strengths of the IMFs of the compounds to predict their relative boiling points.
As was the case for gaseous substances, the kinetic molecular theory may be used to explain the behavior of solids and liquids. In the following description, the term particle will be used to refer to an atom, molecule, or ion. Consider these two aspects of the molecular-level environments in solid, liquid, and gaseous matter:. 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.
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