Interrelations between standard entropy, formation enthalpy and boiling temperature of hydrocarbons

We show that there exists a relationship between the standard entropy and formation enthalpy of hydrocarbon compounds founded purely on the laws of thermodynamics and by invoking the maximum work concept. The validity of the expression obtained for entropy is examined using the properties of 78 hydrocarbon compounds taken from NIST and Knovel databases. A linear regression analysis of the data led to two different sets of values for the coefficients of the proposed relation. Group (I) consists of 54 compounds comprising alkanes, alkenes, alkynes, and aromatics and the remaining 24 hydrocarbons are categorized as Group (II). An additional set of data comprising 33 different hydrocarbons is used as a testing set to examine the predictability of the proposed relation. The average percentage error for all 33 hydrocarbons is found to be 0.5 ± 6.1%. The study also presents derivation of an expression for the normal boiling temperature of hydrocarbons as a function of elemental composition. The accuracy of the boiling temperature relation is assessed by comparing the predicted and measured properties of the same 33 hydrocarbons. On an average basis, the percentage error is found to be −0.3 ± 2.7%. The new relations can be used to predict the standard thermodynamic properties with acceptable accuracy without a need for complex experimental or computational methods.