Apparent molar volumes of aqueous solutions of n-dodecylpyridinium chloride (DDPC) were measured at T = (298.15, 313.15, 328.15, 343.15, 358.15, and 372.05) K at p = 0.3(5) MPa. A mass-action model was used to describe the results and to obtain densities of DDPC solutions at 5 K intervals from T = 283.15 K to T = 393.15 K. Apparent molar heat capacities of aqueous solutions of DDPC were determined at 5 K intervals from T = 283.15 K to T = 393.15 K at p = 0.35 MPa using a fixed-cell, power-compensation, differential-output, temperature-scanning calorimeter. Measurements were made from molalities 0.003 mol . kg(-1) 0.15 mol . kg(-1) for both densities and heat capacities. The same mass-action law model was used to try to describe ail the apparent molar heat capacity results simultaneously.