# Is the P-Cl bond energy same in PCl5 and PCl3?

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?

• Wolfram Alpha does not know apples from oranges when it comes to chemistry. Also, we don't use mathjax in the title. – Ivan Neretin Nov 14 '15 at 7:30
• Hehe :-P!Ok! @IvanNeretin .Do tell your answer also... – user14857 Nov 14 '15 at 7:31
• Of course they are different. I expect the bond in $\ce{PCl3}$ to be stronger. – Ivan Neretin Nov 14 '15 at 8:47
• @IvanNeretin why is it so?And in PCl5 itself are all the bond lengths same or different? – user14857 Nov 14 '15 at 8:59
• 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. – Jan Nov 14 '15 at 13:28

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 $\ce{PCl5}$).