Final answer:
Oxygen or compressed air is not used to pressurize a refrigeration system due to oxygen's inability to be liquefied at room temperature and the impracticality of disrupting the intermolecular forces in compressed air or oxygen.
Step-by-step explanation:
Oxygen or compressed air is never used to pressurize a refrigeration system because of two main reasons:
- Oxygen cannot be liquefied at room temperature by placing it under a large enough pressure to force its molecules together. This is due to the fact that oxygen does not have sufficient energy to attain the activation energy needed to produce water.
- The process of compressing and expanding the gas in a refrigeration system involves a greater and more uniform dispersal of matter. Using compressed air or oxygen would require an input of energy to disrupt the intermolecular forces between the gas molecules, which is not practical for refrigeration purposes.