An ideal monatomic gas at initial temperature T0 (in kelvins)
expands from initial volume V0 to volume 2V0 by each of the five
processes indicated in the T-V diagram of Fig. 20-20. In which
process is the expansion (a) isothermal, (b) isobaric (constant pressure),
and (c) adiabatic? Explain your answers. (d) In which processes
does the entropy of the gas decrease?

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