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Thread: Regarding boiling points and melting points

  1. #1 Regarding boiling points and melting points 
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    Are the two proportional? (ie a substance with a higher boiling point should also have a higher melting point when compared with another substance?)

    I learnt that a branched compound generally has a lower boiling point due to its smaller surface area which leads to fewer interactions of the electron clouds; while a higher melting point is resulted due to its more efficient packing.

    How could that be explained? (esp. the latter)

    Thank you.


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  3. #2  
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    Sounds like it would be a good exercise for you to make a graph, plot BP against MP and see if there is a correlation, from the graph you might discover a formula, a trend or just a forest of dots, you might want to stick to elements or simple compounds for this. :wink:


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  4. #3  
    Forum Senior anand_kapadia's Avatar
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    branched compound
    What are they.
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  5. #4  
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    Quote Originally Posted by anand_kapadia
    branched compound
    What are they.
    like propan-1-ol (branched chain) and butane (straight chain)
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    Forum Freshman Dantak's Avatar
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    Doesn't have anything to do with the topic but propanol is not a branched compound. You wouldn't call propane branched and adding an alcohol to to end of it doesn't make it brached. To keep it simply you would call t-butyl groups branched. A branched compound is an organic compound that has tertiary carbons. Carbons connected to 3 other carbons. Like 3-ethyl-2,5-dimethyl-4-propylheptane. Now that's a branched compound.
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  7. #6  
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    the latter: yes branched or unsaturated molecules do have lower melting and boiling points due to the curved/ bramched nature of their molecules which dont allow them to align perfectly next to each other reducing the amount of Van der Waals and other intermolecular forces which can take place in a similar linear compund. That is the reason why some triglycerides are fats and other oils due to the straightness of the fatty chains i.e highly unsaturated chains have large kinks less surface area in contact less intermoilcular attraction less energy need to break them apart therefore liquid oil less unsaturated chains have mor surface area in contact more intermolecular attractions more energy needed to pull them apart so remain solid
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