Question #9604

I wish to know how to calculate the Enthalpy change for the reaction POCL3.
Thank you.

Expert's answer

You must Use Hess's Law to determine the enthalpy change for the following reaction

P_{4}O_{10}(s) --> P_{4}(s)+ 5O_{2}(g) delta H = +2967 KJ {#2 reversed}

6PCl_{5} --> 6PCl_{3} + 6Cl_{2} delta H = +504 kJ {#3 reversed and multiplied by 6}

P_{4} + 6Cl_{2} --> 4PCl_{3} delta H = -1226 kJ {#1 used as is}

10PCl_{3} + 5O_{2} ---> 10POCl_{3} delta H = -2860 kJ {#4 multiplied by 10}

______________________________________ {added together}

P_{4}O_{10} + 6PCl_{5} --> 10PCl_{3} delta H = -615 kJ

P

6PCl

P

10PCl

______________________________________ {added together}

P

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