1 mole of an ideal gas with CV,m = 5/2 R undergoes transformation either (I) or (II) from an initial temperature (Ti) = 250 K and initial pressure (Pi) = 1.00 bar. CV,m denotes molar heat capacity at constant volume. (I) 1 mol of gas undergoes a reversible adiabatic expansion until the final pressure (Pf) is half of its initial value. The surroundings are at 250 K and 0.500 bar. (II) 1 mol of gas undergoes an adiabatic expansion against a constant external pressure (Pex) of 0.500 bar until the final pressure (Pf) is equal to half of its initial value. The surroundings are at 300 K and 0.500 bar. a) Calculate the change in entropy of the system (ΔSsys) (in unit J K-1 ) for each (I) and (II). b) Calculate the change in entropy of the surroundings (ΔSsur) (in unit J K-1 ) for each (I) and (II). c) Calculate the total change in entropy (ΔStot) (in unit J K-1 ) for each (I) and (II).
1 mole of an ideal gas with CV,m = 5/2 R undergoes transformation either (I) or (II) from an
initial temperature (Ti) = 250 K and initial pressure (Pi) = 1.00 bar. CV,m denotes molar heat
capacity at constant volume.
(I) 1 mol of gas undergoes a reversible adiabatic expansion until the final pressure (Pf) is
half of its initial value. The surroundings are at 250 K and 0.500 bar.
(II) 1 mol of gas undergoes an adiabatic expansion against a constant external pressure
(Pex) of 0.500 bar until the final pressure (Pf) is equal to half of its initial value. The
surroundings are at 300 K and 0.500 bar.
a) Calculate the change in entropy of the system (ΔSsys) (in unit J K-1
) for each (I) and (II).
b) Calculate the change in entropy of the surroundings (ΔSsur) (in unit J K-1
) for each (I) and
(II).
c) Calculate the total change in entropy (ΔStot) (in unit J K-1
) for each (I) and (II).
d) State which of the process [(I) or (II)] is a spontaneous process.
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