You have a cylinder that contains 500 L of the gas mixture pressurized to 2000 psi (gauge pressure). A regulator sets the gas flow to deliver 8.2 L/min at atmospheric pressure. Assume that this flow is slow enough that the expansion is isothermal and the gases remain mixed. How much time will it take to empty the cylinder?

(a) 1 h;

(b) 33 h;

(c) 57 h;

(d) 140 h.

One type of gas mixture used in anesthesiology is a 50%/50% mixture (by volume) of nitrous oxide (N₂O) and oxygen (O₂), which can be premixed and kept in a cylinder for later use. Because these two gases don’t react chemically at or below 2000 psi, at typical room temperatures they form a homogeneous single gas phase, which can be considered an ideal gas. If the temperature drops below -6°C, however, N₂O may begin to condense out of the gas phase. Then any gas removed from the cylinder will initially be nearly pure O₂; as the cylinder empties, the proportion of O₂ will decrease until the gas coming from the cylinder is nearly pure N₂O.