Partialmolarvolumina

Partialmolarvolumina (partial molar volumes) are thermodynamic quantities that describe how the volume of a mixture changes when the amount of one component is varied at constant temperature and pressure. For component i the partial molar volume V̄i is defined as V̄i = (∂V/∂ni)_{T,P,nj}, and the total volume V of a mixture of components satisfies V = Σ ni V̄i. In terms of composition, the molar volume of a mixture Vm equals the mole-fraction-weighted sum Vm = Σ xi V̄i.

Partial molar volumes convey the incremental volume change per mole of a substance added to a mixture and thus reflect intermolecular interactions and packing effects. They are composition-dependent and can differ markedly from pure-component molar volumes; nonideal interactions often produce positive or negative deviations, observed as volume expansion or contraction on mixing.

Experimentally, partial molar volumes are determined from precise density or dilatometric measurements as functions of composition and converted to volume per mole by differentiation. Ultrasonic and scattering techniques, as well as thermodynamic models and molecular simulations, provide complementary estimates. The concept is used in solution chemistry, chemical engineering, and materials science to characterize solvation, hydration, and mixing behavior, and to compute related properties such as excess molar volume and concentration-dependent partial properties.