Question

Thermal stability order of HX is- HF>HCl>HBr>HI [But the order should be HF>HI>HBr>HCl, due vanderwall forces in HI, HBr(due to large size)]. Can you explin me please why this has happened?

Answer 1

Thermal stability is directly proportional to bond dissociation energy.Bond dissociation enthalpy is defined as the energy required to break between two atoms.As we move from fluorine to iodine atomic sizes increases,therefore ,H-X bond length increases.This causes the H-X bond dissociation energy to decrease & hence H-X bonds breaks more easily.Thus the thermal stability is decreased in the order:HF>HCI>HBr>Hl