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Is the $\ce{P-Cl}$ bond energy same in $\ce{PCl5}$ and $\ce{PCl3}$? Why?

According to wolfram alpha both have $\pu{326 kJ mol-1}$ energy. But my study material says that they are not same. I'm confused. Can someone clarify?

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    $\begingroup$ Wolfram Alpha does not know apples from oranges when it comes to chemistry. Also, we don't use mathjax in the title. $\endgroup$ Commented Nov 14, 2015 at 7:30
  • $\begingroup$ Hehe :-P!Ok! @IvanNeretin .Do tell your answer also... $\endgroup$
    – user14857
    Commented Nov 14, 2015 at 7:31
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    $\begingroup$ Of course they are different. I expect the bond in $\ce{PCl3}$ to be stronger. $\endgroup$ Commented Nov 14, 2015 at 8:47
  • $\begingroup$ @IvanNeretin why is it so?And in PCl5 itself are all the bond lengths same or different? $\endgroup$
    – user14857
    Commented Nov 14, 2015 at 8:59
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    $\begingroup$ They can’t be the same, because $\ce{PCl5}$ (in gas phase) has two different $\ce{P-Cl}$ bonds while $\ce{PCl3}$ only has one. $\endgroup$
    – Jan
    Commented Nov 14, 2015 at 13:28

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The $\ce{P-Cl}$ bond in $\ce{PCl3}$ is stronger ($\pu{322 kJ/mol}$) than that in $\ce{PCl5}\ (\pu{260 kJ/mol})$. However the $\pu{326 kJ/mol}$ value comes from the average of all $\ce{P-Cl}$ bonds found in all known molecules containing $\ce{P-Cl}$ bonds (including but not limited to $\ce{PCl3}$ and $\ce{PCl5}$).

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