The greatest positive enthalpy change has PCl₅(g) → P(g) + 5Cl(g)
An enthalpy change is difference between the enthalpy after the chemical reaction has completed.
An enthalpy change of phosphorus(V) chloride (PCl₅) molecule is energy needed for breaking up one molecule of phosphorus(V) chloride into one phosphorus and five chlorine atoms.
In a chemical reaction, chemical bonds are forming and breaking and this cause the transformation of one group of chemical substances to another.
Energy is needed to break chemical bonds in molecules (positive enthalpy change), while during formation of molecule, energy is released (negative enthalpy change)
The stronger are the bonds, more energy is needed and enthalpy change is more positive.
PCl₅ has more bonds to break than PCl₃.
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