Chem 112 Exam AID Course Pack

The main ideas are the same its just that the melting

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Unformatted text preview: , B with B, and A with B need to all be approximately the same strength (or A with B greater). − Note that all of this also applies to solids and gases dissolved in liquids as well. Most gases are not very soluble in water, though, since they have weak intermolecular forces or they wouldn’t be gases in the first place. − If A with B is just a little bit weaker, you still will get a solution forming. In this case, the extra entropy from the different types of molecules being mixed together will make up the difference. Ethan Newton & Barry Zhang for SOS Winter 2012 22 − For example, water (forms H- bonds with itself) will not dissolve hexane (forms London dispersion forces with itself), since the interactions between water and hexane would also be London dispersion forces, which are much weaker than H- bonds. The same is true for any non- polar substance in water; by contrast, water will dissolve most polar molecules, as well as ions. This can also be viewed in terms of enthalpy. - stronger IMFs take more energy to break than weaker IMFs, and release more energy when formed - anything that promotes the formation of stronger IMFs will be favoured and thus spontaneous - anything that does not promote the formation of stronger IMFs will not be favoured, and will not be spontaneous - in the second case, an input of energy (like shaking the container) would be required?] (you will never make it a solution though, since there’s no way you can make it truly homogenous at the molecular level by doing that) When the A- A, B- B, and A- B intermolecular forces are exactly equal (for example, benzene and toluene), then the solution is an ideal solution. Also, considering the case when gases are in solution, we get another gas law (Henry’s Law): the amount of gas dissolved in the solvent is directly proportional to the pressure above the solvent that the gas exerts. The constant of proportionality is KH, the Henry’s Law Parameter, which is a constant for every different solvent. CA = KHPA Fraction graphs) are graphs in which the x- axis represents mole fraction for two substances. (Take the example of water and acetone). - the graph goes from 0 to 1 for water, and 1 to 0 for acetone - 0 represents pure acetone, and 0.2 represents 80% acetone and 20% water (by number of molecules), 0.5 represents equal moles of each, 1 represents pure water, etc The y- axis of a fraction graph can be anything. (When the y- axis is temperature or pressure, you have a two- component phase diagram, although out of those two, you are only responsible for the...
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This note was uploaded on 10/02/2012 for the course CHEM 112 taught by Professor Carran during the Winter '08 term at Queens University.

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