6. Answer the following questions for the following constant pressure situations

Question

6. Answer the following questions for the following constant pressure situations (see graphs, below) a. 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) b. Based on the RIGHT graph, estimate: 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) Entropy vs Temperature for o 200 0.3 150 0.2 Solid I 1000 Gas Solid II 0.1 50 Liquid -Solid III 100 200 100 150 200 Temperature (K) Temperature (K)

Explanation / Answer

a)

At the temperature of 200K, the graph of Au is higher than the graph of Cu, hence the Au has higher absolute entropy then Cu at 200K

b)

The enthalpy of vaporization can be calculated from 60 x 60 = 3600J/mol

                                                                                                  = 3.6 KJ/mol,

hence the entropy of vaporizatio must be close to this number

in order to calculate the heat capacity of liquid oxygen, we need to look on the line joininig red and pink area, the

value on that point is 1.7 KJ/mol

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