Phosphorus pentachloride is a white solid that sublimes (vaporizes without melting) at about 100 degrees C. At higher temperatures, the PCl5 vapor decomposes to give phosphorus trichloride and chlorine.
How could gas-density measurements help to establish that PCl5 vapor is decomposing?
Gas-density measurements can be used to establish that PCl5 vapor is decomposing by comparing the density of the PCl5 vapor at different temperatures. Here's how it works:
1. Obtain gas-density measurements: Start by collecting gas-density measurements of PCl5 vapor at different temperatures. This can be done using a gas-density measuring device, such as a gas manometer or a digital gas density meter.
2. Determine the density of PCl5 vapor: Measure the density of PCl5 vapor at the initial temperature, i.e., the temperature at which PCl5 is stable and does not decompose. This will serve as a reference density.
3. Heat the PCl5: Gradually increase the temperature while continuously measuring the density of the PCl5 vapor. As the temperature increases, the PCl5 vapor will start to decompose.
4. Monitor density changes: Observe any changes in the density of the PCl5 vapor as the temperature increases. If the PCl5 vapor is decomposing, the density of the gas will decrease.
5. Compare densities: Compare the densities of the PCl5 vapor at different temperatures to the reference density. If the density decreases with increasing temperature, it indicates that the PCl5 vapor is decomposing into other gases.
6. Identify decomposition products: Use the known decomposition reaction of PCl5 to interpret the observed decrease in density. In this case, the decomposition of PCl5 produces phosphorus trichloride (PCl3) and chlorine gas (Cl2). So, a decrease in density suggests the formation of PCl3 and Cl2 gases.
In conclusion, by measuring the density of PCl5 vapor at different temperatures and observing a decrease in density, we can establish that PCl5 vapor is decomposing into phosphorus trichloride and chlorine gas.