Thermal Stability of Hydrogen Halides
by gg kento

1. Definition
1.1. Thermal stability refers to the ability of a compound to resist decomposition upon heating
1.2. It is influenced by bond strength (bond dissociation enthalpy)
2. Hydrogen Halides in order of Thermal Stability
2.1. HF (most stable) > HCl > HBr > HI (least stable)
3. Based on Bond Strength
3.1. Bond Strength Trend: H–X bond strength decreases down the group (F > Cl > Br > I).
3.2. Bond Dissociation Energy (kJ/mol): H–F: 570 (strongest) H–Cl: 432 H–Br: 366 H–I: 298 (weakest)
3.3. Weaker bonds break more easily, leading to lower thermal stability for heavier halides.
4. Factors affecting bond strength
4.1. Bond Length
4.1.1. Increases down the group (F < Cl < Br < I) due to increasing atomic size.
4.1.2. Longer bonds are weaker, making them easier to break.
4.2. Electronegativity Difference
4.2.1. Fluorine (F) is the most electronegative, creating the strongest H–X bond.
4.2.2. Electronegativity difference decreases down the group, weakening the bond.