Question

Consider the flasks diagrammed below. What is the total pressure in torr after the stopcock between the two flasks is opened? He(g)---> V=1.25L and P=0.300atm and Ar(g)---> V=2.50L and P=233 torr.

Answer 1

First, let's convert all the pressures to the same unit. We will use torr since one of them is already in torr.

1 atm = 760 torr, so 0.300 atm = 0.300 * 760 = 228 torr.

Now we have:

He(g): V = 1.25 L, P = 228 torr
Ar(g): V = 2.50 L, P = 233 torr

When the stopcock between the flasks is opened, the gases will mix and the final pressure can be found using the formula for partial pressures:

P_total = P_He + P_Ar

To calculate the partial pressures, we first need the total volume:

V_total = V_He + V_Ar = 1.25 L + 2.50 L = 3.75 L

Now we have to find the moles of each gas using the ideal gas law equation, PV = nRT. We'll assume a constant temperature and use R = 62.36 L * torr / mol * K since we're using torr and L.

He(g): 228 torr * 1.25 L = n * 62.36 L * torr / mol * K
n_He = 228 * 1.25 / 62.36 = 4.583 moles

Ar(g): 233 torr * 2.50 L = n * 62.36 L * torr / mol * K
n_Ar = 233 * 2.50 / 62.36 = 9.324 moles

Now, we can use the total volume and total moles to find the new pressure after the gases mix:

P_total * 3.75 L = (4.583 + 9.324) * 62.36 L * torr / mol * K
P_total = (4.583 + 9.324) * 62.36 / 3.75 = 242.40 torr

The total pressure after the stopcock is opened and the gases mix is approximately 242.40 torr.