Final answer:
If PCl is changed to 0.8, it means pressure is increased, and if temperature and number of moles remain constant, the molar volume (Vm) of the gas will decrease according to Boyle's Law.
Step-by-step explanation:
When the partial pressure (PCl) is changed to 0.8, and we are considering a gas represented within the equation PV = nRT where P is the pressure, V is the volume, n is the number of moles, R is the gas constant, and T is the temperature, we need to understand the relationship between pressure and molar volume (Vm). If temperature (T) and number of moles (n) are held constant, and the pressure is increased (as indicated by PCl changing to 0.8), the molar volume (Vm) will decrease according to Boyle's Law which states that the volume of a given amount of gas held at constant temperature varies inversely with the applied pressure.
The scenario also seems to discuss ideal gas behavior versus real gas behavior. Deviations from the ideal gas law can be observed when the pressure begins to rise, leading to the volume being less than expected due to attractive forces between gas molecules. Therefore, a real gas will have a different molar volume compared to that predicted by the ideal gas law under these conditions.