Final answer:
If the partial pressure P Cl is increased to 0.8, the molar volume V m would decrease according to the Ideal Gas Law, provided that temperature and amount of substance remain constant.
Step-by-step explanation:
If P Cl is changed to 0.8, presumably referring to the partial pressure of chlorine gas (Cl2), and you want to understand what happens to the molar volume Vm, we need to consider the Ideal Gas Law, which is represented by the equation PV = nRT.
Here, P stands for pressure, V is volume, n is the number of moles, R is the ideal gas constant, and T is the temperature. For a given quantity of gas at constant temperature and amount of substance (n), if the pressure P increases, the volume V must decrease in order to maintain the equation balance.
Given the constants and temperature (presumably kept constant), you can solve for the molar volume Vm by rearranging the Ideal Gas Law to V = \frac{nRT}{P}.
With an increase in the pressure P, the volume V will decrease, suggesting that the molar volume Vm will also decrease. Therefore, if P Cl is changed to 0.8, it would lead to a decrease in the molar volume Vm assuming that the pressure that is being referred to is the total pressure exerted by the gas.