A new thermodynamic function for binary mixtures: The co-molar volume.

Area of Science:

• Thermodynamics
• Physical Chemistry
• Computational Chemistry

Background:

• Partial molar volumes are standard thermodynamic properties but lack intuitive physical meaning.
• Traditional partial molar volumes represent volume derivatives, not actual molecular space occupied.
• Intrinsic volumes, calculable via simulations, offer a direct measure of molecular space.

Purpose of the Study:

• To develop a new theory connecting partial molar volumes with intrinsic molecular volumes.
• To define a novel thermodynamic variable, the co-molar volume, bridging these two concepts.
• To provide a more intuitive physical interpretation of thermodynamic properties in mixtures.

Main Methods:

• Development of a new thermodynamic theory.
• Application of Euler's theorem for homogeneous functions.
• Utilizing molecular dynamics simulations with Voronoi tessellation to determine intrinsic volumes.

Main Results:

• Established a theoretical framework relating partial molar volumes to intrinsic (Voronoi) volumes.
• Introduced the co-molar volume as a new thermodynamic variable.
• Demonstrated the validity of the co-molar volume through molecular dynamics simulations.

Conclusions:

• The co-molar volume successfully bridges the gap between traditional thermodynamic properties and physically determined molecular volumes.
• This new variable offers enhanced insights into the spatial contributions of components in mixtures.
• Co-molar volume shows a relationship to co-moving velocity in two-phase flow systems.