One type of gas mixture used in anesthesiology is a 50%/50% mixture (by volume)
ID: 3278481 • Letter: O
Question
One type of gas mixture used in anesthesiology is a 50%/50% mixture (by volume) of nitrous oxide (N_2 O) and oxygen (O_2), 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 degree C, however, N_2O may begin to condense out of the gas phase. Then any gas removed from the cylinder will initially be nearly pure O_2: as the cylinder empties, the proportion of O_2 will decrease until the gas coming from the cylinder is nearly pure N_2O. In a test, the valve of a 500-L cylinder full of the gas mixture at 2000 psi (gauge pressure) is opened wide so that the gas rushes out of the cylinder very rapidly. Why might some N_2O condense during this process? This is an isochoric process in which the pressure decreases, so the temperature also decreases. Because of the rapid expansion, heat is removed from the system, so the internal energy and temperature of the gas decrease. This is an isobaric process, so as the volume increases, the temperature decreases proportionally. With the rapid expansion, the expanding gas does work with no heat input, so the internal energy and temperature of the gas decrease.Explanation / Answer
Option D is the correct answer.
The process is a rapid expansion or adiabatic expansion. For adiabatic process, heat exchanged between system and the surrounding is zero. The work done by the gas is at the expense of internal energy. So an expanding gas will cool the system by spending its internal energy.
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