Question

Questions A37- A39 relate to a phase change ('pc") for which ApcFl- +25 kJ mol and pS+50 J - mol, independent of temperature. A37. What is the value of the temperature, in K, at which the phase change occurs? a) 0.002 b) 0.5 c) 2 A38. For the temperature at which the phase change occurs, what is the value, in J K-1 mol1, of the entropy change of the surroundings? a) 50 b) 0 c) +25 d) +50 A39. For the temperature at which the phase change occurs, what is the value, in kJ mor-, of the Gibbs energy change of the system? a) +50 b) +25 c) d)-25 Page 7 of 19

Answer 1

Hello Dear Friend, we will use Gibbs free energy relationship to solve this problem.

ΔG^o = ΔH^o - TΔS^o

at phase change ΔG^o = 0 (almost we will consider as system at equilibrium)

37)

0 = ΔH^o - TΔS^o since ΔG^o = 0 and 1 kJ = 1000 J, so 25 kJ/mol = 25000 J/mol

T = ΔH^o / ΔS^o = (25 kJ/mol) / 50 J/mol.K = [25000 J/mol] / [50 J/mol.K] = 500 K

T = 500 K

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38) ΔS_system = - ΔS_surroundings at equlibrium

Hence ΔS_surroundings = -50 J/mol.K

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39) as discussed above at phase change (equilibrium) gibbs free energy change is always zero according to definition.

ΔG^o = 0

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Hope this helped you!

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