Please help me with the answers of these questions:
(a) Suggest why the expansion of air into a region of low pressure is an endothermic process? (b) Gases like CO2 can be liquified at room temp just by pressuring them. Why does the application of pressure causes the gas to liquify? (c) Gases can only be liquified by pressure alone if their temp is below their critical temp Tc. Above Tc, no amount of pressure will liquify a gas. Give an explanation.

Question

Please help me with the answers of these questions:
(a) Suggest why the expansion of air into a region of low pressure is an endothermic process? (b) Gases like CO2 can be liquified at room temp just by pressuring them. Why does the application of pressure causes the gas to liquify? (c) Gases can only be liquified by pressure alone if their temp is below their critical temp Tc. Above Tc, no amount of pressure will liquify a gas. Give an explanation.