In Section 2.3, we learned about reversible and irreversible processes in the context of a piston–cylinder assembly undergoing isothermal expansion and compression processes. Four of these processes are summarized in Figure 3.2:

(i) Irreversible expansion, process A 

(ii) Irreversible compression, process B 

(iii) Reversible expansion, processes E 

(iv) Reversible compression, processes F

Calculate Δsuniv for each of these isothermal processes and show that the result is consistent with the second law of thermodynamics.

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m= 1020 kg A = 0.1 m 1 mol of pure, ideal gas Irreversible 'external' pressure (bar) atm Fexternal/area or MT = 1020 kg VS. 0.4 m expansion Irreversible Reversible am .04 Molar volume (m/mol) A = 0.1 m 1 mol of pure, ideal gas Reversible compression Irreversible Pat .08 atm Carnot cycle: 0.4 m QH- (a) Process I: Isothermal Expansion/Compression Hot reservoir, TH Isothermal expansion Cold reservoir, To Irreversible vs. Adiabatic expansion Carnot engine Hot reservoir, TH 3881 QH CHE HE HE KE Cold reservoir, To Isothermal expansion Reversible (b) Process II: Thermal Heat Engine Adiabatic expansion Wnet 4 State State 1 Figure 3.2 Illustration of irreversible and reversible processes. (a) Mechanical process of iso- thermal expansion/compression. (b) Thermal process in which work can be obtained from a Car- not engine.