The thermodynamic equilibrium of the liquid-phase bimolecular dehydration of I-pentanol to di-n-pentyl ether (DNPE) and water was studied in the temperature range of 423-463 K over Amberlyst 70. Furthermore, the equilibrium position of two side reactions could be followed, DNPE decomposition to I-pentanol and I-pentene and isomerization of I-pentene to 2-pentene. The etherification reaction proved to be slightly exothermic, with an enthalpy change of reaction at 298.15 K of -(3.8 +/- 0.6) kJ mol(-1). From this value, the standard formation enthalpy and molar entropy of DNPE were computed to be -(421.1 +/- 1.2) kJ mol(-1) and 473.71 J (K.mol)(-1), respectively. The enthalpy changes of the reaction of DNPE decomposition to I-pentene and I-pentanol and I-pentene isomerization to 2-pentene were 63.4 +/- 0.9 and -19.7 +/- 2.1 kJ mol(-1), respectively.