When a sample is above critical temperature and above critical pressure, it is a supercritical fluid.
What happens when a sample is above critical temperature but below critical pressure? What phase is that?
What happens when a sample is above critical pressure but below critical temperature? What phase is that?
"Discuss what would be observed as a sample of water is taken along a path that encircles and is close to its critical point."
Obviously, when a sample crosses the gas-liquid phase boundary, standard evaporation or condensation will occur. But how about the rest of that cycle?
i don't know the answer,helping please
When a sample is above the critical temperature but below the critical pressure, it is in the gas phase. This is because the sample has enough thermal energy to remain as a gas even though the pressure is below the critical pressure. At this point, the sample cannot exist as a liquid, regardless of the pressure.
Conversely, when a sample is above the critical pressure but below the critical temperature, it is in the liquid phase. In this case, the pressure is high enough to keep the sample in the liquid state even though the temperature is below the critical temperature. It cannot exist as a gas under these conditions.
Now, let's discuss what can be observed as a sample of water is taken along a path near its critical point. The critical point for water is approximately 374 degrees Celsius (about 705 degrees Fahrenheit) and 218 atmospheres of pressure. As the sample approaches the critical point, several interesting phenomena occur:
1. Density Changes: The density of water near the critical point increases significantly, reaching a maximum at the critical point. Along the path near the critical point, slight changes in pressure or temperature can cause significant variations in density.
2. Opacity: Water near its critical point becomes highly opaque or turbid due to the presence of small droplets. This phenomenon is known as critical opalescence and is caused by the fluctuations in density.
3. Efficiency of Heat Transfer: As the sample moves closer to the critical point, the efficiency of heat transfer increases, which means that it becomes easier to transfer heat into or out of the system. This property can be advantageous in heat transfer applications.
4. Continuous Phase Transition: Near the critical point, there is no distinct phase transition between the liquid and gas phases. Instead, there is a gradual change in properties, such as density, compressibility, and dielectric constant.
It's important to note that while specific observations depend on the substance and its phase diagram, these are some general characteristics that can be observed near the critical point of a substance like water.