Thermodynamics NOTE: i have posted this question twice already and ONLY NEED PAR

Question

Thermodynamics NOTE: i have posted this question twice already and ONLY NEED PART B ANSWERED this time.
6. Answer the following questions for the following constant pressure situations (see graphs, below) Based on the LEFT graph, which element-copper (Cu) or gold (Au)--has the higher absolute entropy at a temperature of 200 K. Explain. (Oxtoby 13.51) Based on the RIGHT graph, estimate: i) the enthalpy of vaporization for oxygen and ii) the heat capacity cp of liquid oxygen at 70 K. Indicate what point(s) you use from the plot when you make your estimate. (Figure 05-10 from EDR) a. b. Entropy vs Temperature for O,2 200 0.3 150 0.2 Solid I 100 Gas Solid II 0.1 Solid III 100 200 50 100 150 200 Temperature (K) Temperature (K)

Explanation / Answer

Solution:

Part b) 1)

At constant pressure,

dQ= dH always

And we need to find out enthalphy of vaporization means H or Q required to change oxygen from liquid form to vapour

if see in graph at 100K there is vertical line which corresponds to entropy change at constant temp

entropy change is (170-90) = 80 J/k/mol

so corresponding heat change or enthalphy will be dQ or dH = dS(T)

                                                                                                  =80 x100 J/mol

                                                                                                  =8 kJ/mol

2)

dS= dQ/T

dS = Cp dT/T

integrating both side taking conditions 1 & 2

S2-S1 = Cp log(T2/T1)

so Cp = (S2-S1)/ log (T2/T1)

In given problem we need to calculate Cp at 70K so T2 is 70K

taking T1=10 K from where vertical graph starts

using graph approx S2-S1 is 1925 J/k/mol (area of graph uoto 70K)

Cp = 1925/log(70/10)

       = 2277.84 J/k/mol

       =2.27 kJ/k/mol

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