new member Posted June 19, 2009 Report Share Posted June 19, 2009 Does melting point of alkane increase or decrease with branching? EK emphasized that mp increases with branching but Kaplan said mp decreases with branching... Link to comment Share on other sites More sharing options...
sv3 Posted June 19, 2009 Report Share Posted June 19, 2009 Does melting point of alkane increase or decrease with branching? EK emphasized that mp increases with branching but Kaplan said mp decreases with branching... really? Ek said that? I have Ek and in my books they correctly state that MP decreases with branching. Branching reduces surface area avail. for intermolecular forces. Look at it another way....more branching makes it harder to crystallize so its freezing point goes down (which means its MP also goes down) sv3 Link to comment Share on other sites More sharing options...
skp1187 Posted June 19, 2009 Report Share Posted June 19, 2009 My EK book (7th edition) says the same thing as New Member. So is EK's wrong on this??? Link to comment Share on other sites More sharing options...
sv3 Posted June 19, 2009 Report Share Posted June 19, 2009 My EK book (7th edition) says the same thing as New Member. So is EK's wrong on this??? Sorry my Ek book is wrong as well. I have TPR too and they also state MP goes DOWN with increased branching. I'll take kaplan + TPR + logic over Ek. Link to comment Share on other sites More sharing options...
interleukin Posted June 19, 2009 Report Share Posted June 19, 2009 Boiling Point: branched molecules are more compact, less surface area to interact with other molecules, more branching --> lower boiling point Melting point: the more branched the alkane is the less flexible it is, it will make better crystals. So it will take more energy to melt them from solid to liquid. Therefore, increased branching increases the melting point Hope this clarifies things a bit. It is easy to accidentally mess up the melting/boiling point terms! Link to comment Share on other sites More sharing options...
sv3 Posted June 19, 2009 Report Share Posted June 19, 2009 Boiling Point: branched molecules are more compact, less surface area to interact with other molecules, more branching --> lower boiling point Melting point: the more branched the alkane is the less flexible it is, it will make better crystals. So it will take more energy to melt them from solid to liquid. Therefore, increased branching increases the melting point Hope this clarifies things a bit. It is easy to accidentally mess up the melting/boiling point terms! Hey, not sure if that's correct about the MP. In order to crystallize into a lattice, the more orderly arranged the lattice the better. Branching impedes this. It makes logical sense plus its what I've gathered from TPR. Pretty sure Ek is wrong here but i've seen crazier things happen than me being wrong haha. Link to comment Share on other sites More sharing options...
new member Posted June 19, 2009 Author Report Share Posted June 19, 2009 thank you all for the speedy reply! Link to comment Share on other sites More sharing options...
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