Entropy is a thermodynamic parameter that measures the disorder or randomness of a system. In general, gases with greater molecular weights have greater entropy. Thus, the entropy energies are in the order: 

• HF 173.779 ± 0.003 J K-1mol-1 
• HCl: 186.9 J K-1mol-1
• HBr: 198.7 J K-1mol-1
• HI: 206.6 J K-1mol-1 . Consequently, HI has the highest entropy value while HF has the least because the greater the molecular weights the greater the entropy value.