The critical temperature of water is 374 °C (705 °F). This specific temperature marks a unique point where water can no longer exist as a distinct liquid phase, regardless of the pressure applied.
Understanding the Critical Point
The critical temperature is a fundamental thermodynamic property. It is part of what is known as the **critical point**, a specific combination of temperature and pressure at which the boundary between the liquid and gas phases of a substance disappears. Above this temperature, a substance exists as a **supercritical fluid**, exhibiting properties of both a gas and a liquid.For water, this phenomenon occurs at:
- Critical Temperature: 374 °C (705 °F)
- Critical Pressure: 218 atmospheres (approximately 22.06 MPa or 3,200 psi)
At and above these conditions, the density of liquid water becomes equal to the density of water vapor, making the two phases indistinguishable. There's no longer a clear meniscus separating the liquid from the gas.
| Property | Value |
|---|---|
| Critical Temperature | 374 °C (705 °F) |
| Critical Pressure | 218 atmospheres (22.06 MPa) |
| Phase above Critical Point | Supercritical Fluid |
The Significance of Supercritical Water
When water is heated above its critical temperature and pressurized above its critical pressure, it transforms into supercritical water. This state has fascinating and highly useful properties that differ significantly from ordinary liquid water or steam.Key characteristics of supercritical water include:
- Enhanced Solvent Power: Supercritical water acts as an excellent solvent for nonpolar organic compounds, which are typically insoluble in normal water. Conversely, it becomes a poor solvent for ionic salts, which are highly soluble in liquid water.
- Tunable Properties: Its density and solvent properties can be "tuned" by adjusting the temperature and pressure, allowing for precise control over chemical reactions and separation processes.
- High Diffusivity and Low Viscosity: It possesses gas-like diffusivity and liquid-like density, making it an efficient medium for mass transfer and chemical reactions.
Applications of Supercritical Water
The unique properties of supercritical water have led to its application in various industrial and environmental processes:- Supercritical Water Oxidation (SCWO): This process efficiently destroys hazardous organic wastes, including toxic industrial pollutants and municipal sludge. Organic compounds are completely oxidized into harmless substances like carbon dioxide, water, and nitrogen gas.
- Supercritical Water Gasification (SCWG): Used to convert biomass and organic waste into valuable gaseous fuels (e.g., hydrogen, methane).
- Extraction Processes: Supercritical water can be used to extract useful compounds from natural products or to separate components in industrial mixtures.
- Chemical Synthesis: It serves as a green solvent and reaction medium for various chemical syntheses, offering advantages such as faster reaction rates and higher yields.
Understanding the critical temperature of water is crucial for designing and optimizing these advanced technologies that harness the unique capabilities of supercritical water. For more information on the critical point and supercritical fluids, you can explore resources like Wikipedia's Critical Point (thermodynamics) and Supercritical water.
