We have used a vibrating-tube densimeter to investigate the densities and volumetric properties of aqueous solutions, and a fixed-cell scanning calorimeter to measure aqueous solution heat capacities. Solutions investigated include sugars, neutral weak acids and bases, neutralized acids and bases, neutral and protonated amino acids, surfactants, and both strong and ion-paired electrolytes. We have made measurements at molalities m from 0.005 mol·kg −1 to 0.5 mol·kg −1 , at temperatures T from 278.15 K to 393.15 K, and at the pressure p = 0.35 MPa. We have calculated the apparent molar volumes V φ and apparent molar heat capacities C p,φ of the solutions and fit them by regression to equations that describe the surfaces (V φ , T, m) and (C p,φ , T, m). These results reflect changes and differences in both solute-solute and solute-solvent interactions. Standard state partial molar volumes V 2 ° and heat capacities C p,2 ° were estimated by extrapolation to the m = 0 mol·kg −1 plane of the fitted surfaces. We have calculated (Δ r ,C p,m , T, m) surfaces for various proton dissociation reactions, and we have created surfaces representing (Δ r H m , T, m) and (pQ a , T, m) by integration of our (Δ r C p,m , T, m) surfaces using values for (Δ r H m , m) and (pK a , m) at a reference T as integration constants. We have also created surfaces representing (Δ r S m , T, m) and (Δ r V m , T, m) for these dissociation reactions.