A statistical thermodynamic approach to sonochemical reactions.

Area of Science:

• Physical Chemistry
• Chemical Thermodynamics
• Acoustic Chemistry

Background:

• Sonolysis of carbon dioxide (CO2) involves complex reactions under extreme conditions within cavitation bubbles.
• Understanding the thermodynamic favorability of these reactions is crucial for predicting product formation.

Purpose of the Study:

• To calculate equilibrium constants for CO2 sonolysis, O2 formation, and H2O formation under simulated cavitation bubble conditions.
• To determine the most thermodynamically favorable locations for these reactions within the bubble.

Main Methods:

• Statistical thermodynamics was employed to calculate equilibrium constants (K).
• Calculations were performed across a range of temperatures (ambient to 15200 K) and pressures (ambient to 300 bar) at 300 kHz.
• Reaction locations were proposed based on thermodynamic favorability.

Main Results:

• CO2 decomposition is thermodynamically favored at 15200 K and 1 bar (K1=1.52 x 10^6).
• O2 formation is not expected (K2 max 1.8 x 10^-8), while H2O formation is highly favored (K3=3.4 x 10^47 at 298 K and 300 bar).
• CO2 decomposition favors the bubble shell, and H2O formation favors the bubble wall.

Conclusions:

• Thermodynamic calculations provide insights into reaction pathways during CO2 sonolysis.
• Water formation is significantly more favorable than oxygen formation under studied conditions.
• A small fraction of cavitation bubbles are efficient for CO2 sonolysis, suggesting reaction efficiency limitations.