Passage
Nitrogen is extremely cold in its liquid phase. It is used in the cryopreservation of small tissue samples and in cryosurgery to freeze and destroy diseased tissues. Liquid nitrogen can be produced from nitrogen gas using the Hampson-Linde cycle (Figure 1) .
Figure 1 Hampson-Linde cycle apparatus used to liquefy nitrogenThe cycle begins by compressing nitrogen gas and forcing it through a coil in an external cooler that contains dry ice. The gas proceeds to a heat exchanger, where it cools further due to the countercurrent heat exchange with colder nitrogen gas returning from a later stage of the cycle; this process is known as regenerative cooling. The gas is subsequently forced through a narrow valve, where it expands and cools significantly upon exiting. As a result, a portion of the gas becomes liquefied.The temperature change of the gas exiting the valve is described by the Joule-Thomson effect, which occurs without heat transfer with the surroundings. Finally, the liquefied nitrogen is collected, and the remaining gas is sent through the regenerative cooler back to the compressor to reenter the cycle. The physical properties of nitrogen are given in Table 1.Table 1 Thermal Properties of Nitrogen

-The compressor exerts a pressure of 400 Pa to compress nitrogen gas from 3 L to 1 L. If no heat transfer occurs, how much will the internal energy of the gas change? (Note: 1 m³ = 1000 L.)

Question

Passage
Nitrogen is extremely cold in its liquid phase. It is used in the cryopreservation of small tissue samples and in cryosurgery to freeze and destroy diseased tissues. Liquid nitrogen can be produced from nitrogen gas using the Hampson-Linde cycle (Figure 1) .

Figure 1 Hampson-Linde cycle apparatus used to liquefy nitrogenThe cycle begins by compressing nitrogen gas and forcing it through a coil in an external cooler that contains dry ice. The gas proceeds to a heat exchanger, where it cools further due to the countercurrent heat exchange with colder nitrogen gas returning from a later stage of the cycle; this process is known as regenerative cooling. The gas is subsequently forced through a narrow valve, where it expands and cools significantly upon exiting. As a result, a portion of the gas becomes liquefied.The temperature change of the gas exiting the valve is described by the Joule-Thomson effect, which occurs without heat transfer with the surroundings. Finally, the liquefied nitrogen is collected, and the remaining gas is sent through the regenerative cooler back to the compressor to reenter the cycle. The physical properties of nitrogen are given in Table 1.Table 1 Thermal Properties of Nitrogen

-The compressor exerts a pressure of 400 Pa to compress nitrogen gas from 3 L to 1 L. If no heat transfer occurs, how much will the internal energy of the gas change? (Note: 1 m³ = 1000 L.)

Quizplus · Accepted Answer

11ecba2d_12fc_ba96_a3bf_f56f13d3c928_MD0008_00 The internal energy of a system is the total energy stored in its molecules and is related to its temperature. Energy cannot be created nor destroyed; it can only transfer from one form to another. From the First law of thermodynamics, the change in internal energy (ΔU) is the sum of the amount of heat (Q) transferred to the system and the work (W) done to the system by the surroundings: 11ecba2d_12fc_e1a7_a3bf_79880320fccf_MD0008_00 In this case, nitrogen gas is considered the system and the compressor is considered the surroundings. No direct heat transfer occurs between the system and the surroundings (Q = 0). Despite this, the temperature of the gas increases because its internal energy increases by the amount of work done by the compressor: 11ecba2d_12fc_e1a8_a3bf_f5cb5d525f7e_MD0008_00 The work associated with the expansion or contraction of a gas is known as pressure-volume work, which is calculated as the product of the external pressure (P) and the change in volume (ΔV): 11ecba2d_12fc_e1a9_a3bf_3bebf6ebe294_MD0008_00 The work done by the compressor is positive because the compressor adds energy to the gas by compressing it from a volume of 3 L to 1 L (ΔV = 2L) at a pressure of 400 Pa. Converting 2 L to cubic meters (m³) results in: 11ecba2d_12fc_e1aa_a3bf_3bdb2ef4a28b_MD0008_00 Consequently, the work done on this gas is: 11ecba2d_12fc_e1ab_a3bf_5dd44535b033_MD0008_00 11ecba2d_12fc_e1ac_a3bf_55f701c64738_MD0008_00 Therefore, the internal energy of the gas increases by 0.8 J as the nitrogen gas is compressed from a volume of 3L to a volume of 1 L (Choice A). Educational objective: The internal energy of a system increases when heat is transferred to the system and when work is done on the system (ΔU = Q + W). For a system of gases, the amount of work done is equal to the product of the external pressure and change in volume (W = PΔV).

Passage Nitrogen Is Extremely Cold in Its Liquid Phase. It Is