Are homodesmotic reactions exothermic reactions?
Homodesmotic reactions can be either exothermic or endothermic.
They may be hypothetical reactions, that is, ones that could never occur.
They are used in thermodynamic calculations, so they can be written in a forward or reverse direction.
Depending on the direction, they can be either exothermic or endothermic.
An example of a homodesmotic reaction involving cyclopropane is
cyclo-(CH₂)₃ + 3CH₃-CH₃ → 3CH₃CH₂CH₃
#ΔH°#= -110.9 kJ/mol
If we wrote the equation in the reverse direction, the process would be endothermic.