For each of the following scenarios, use a calculation to predict whether or not
ID: 1047930 • Letter: F
Question
For each of the following scenarios, use a calculation to predict whether or not it will occur spontaneously. (For some cases you may need to use data from Appendix A in your textbook.)
a) 5.0 L of an ideal gas (Cv,m = 5/2 R) in a balloon at 1.5 atm, 298 K undergoes isothermal expansion against 1.0 atm until the final pressure of the gas equals the external pressure.
b) The combustion reaction for glucose at 298 K carried out in a bomb calorimeter.
c) Sublimation of 0.50 mol of dry ice at 277 K (Tsub = 277 K, Ho sub = 25 kJ/mol) that is left out in a room held at 298 K.
Explanation / Answer
a) 5.0 L of an ideal gas (Cv,m = 5/2 R) in a balloon at 1.5 atm, 298 K undergoes isothermal expansion against 1.0 atm until the final pressure of the gas equals the external pressure.
dS = n*R*ln(V2/V1)
n = PV/(RT) = 5*1.5/(0.082*298) = 0.30692421 mol
V1P1 = V2P2
V2/V1 = P1/P2 = 1.5/1
dS = n*R*ln(V2/V1) = 0.307* 8.314 * ln(1.5/1) = 1.034 J/molK
S system > 0
Q = nRT*ln(V2/V1) = 0.306*8.314*298*ln(1.5*1) = 307.398 J
dSsurroundings = -Q/T = -307.398/ 298 = -1.031
Suniverse = -1.031 + 1.034 = 0.003
PRocess is in equilibrium most likely
b)
combustion --> exothermic process, so
G = dH - TdS
dH is negative, and dS increases, so this is always favoured
c)
Ssurroundings = -Q/T= 0.5*25 /(277) = 0.045126 J/K
Ssystem = Q/T =
this is in equilbirium
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