Thermodynamic properties of urea-hydrocarbon adducts. Part 2.—Heat capacities of adducts of n-pentadecane and 2-methyl-pentadecane from 12 to 300°K

Abstract

The heat capacities of the adducts of urea with n-pentadecane and 2-methyl-pentadecane have been measured from 12 to 300°K. The n-pentadecane adduct showed a region of anomalously high heat absorption at 158.4°K; the adduct of the branched-chain paraffin, on the other hand, had no significant thermal anomaly. The entropies of both adducts at 298.15°K have been calculated. A comparison is made of the entropies of adduction of n-C₁₅H₃₂, n-C₁₀H₂₂, n-C₁₂H₂₆ and n-C₁₆H₃₄ as calculated from the heat capacity data with the corresponding values obtained from equilibrium constant measurements by Redlich. The discrepancies between the two sets of values are within the limits of error set by the equilibrium constant data for the decane compound, but for the other substances the values from the heat capacity data are up to 22 % smaller in magnitude.