Answer to Question #9604 in Inorganic Chemistry for Lorenzo

Question

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

Thank you.

Answer 1

You must Use Hess's Law to determine the enthalpy change for the following reaction
P₄O₁₀(s) --> P₄(s)+ 5O₂(g) delta H = +2967 KJ {#2 reversed}
6PCl₅ --> 6PCl₃ + 6Cl₂ delta H = +504 kJ {#3 reversed and multiplied by 6}
P₄ + 6Cl₂ --> 4PCl₃ delta H = -1226 kJ {#1 used as is}
10PCl₃ + 5O₂ ---> 10POCl₃ delta H = -2860 kJ {#4 multiplied by 10}
______________________________________ {added together}

P₄O₁₀ + 6PCl₅ --> 10PCl₃ delta H = -615 kJ