Two crystalline forms of white phosphorus are known. Both forms contain P_4 mole
ID: 1019778 • Letter: T
Question
Two crystalline forms of white phosphorus are known. Both forms contain P_4 molecules, but the molecules are packed together in different ways. The a form is always obtained when the liquid freezes. However, below -76.9 degree C, the a form spontaneously converts to the beta form. P_4(s, rightarrow P_4(s, beta) Indicate which of the following statements are true or false, with regard to the above process. At -76.9 degree C, Delta G for this process is less than zero. At -76.9 degree C, the two solid phases cannot coexist. The a phase has the more ordered crystalline structure. The sign of Delta H for this process is positive. The sign of Delta S for this process is positive. Above -76.9 degree C, the sign of Delta G for this process is negative. cf Section 10.7 Free Energy in Zumdahl "Chemical Principles" 7th ed.Explanation / Answer
A.Accordingly this is a spontaneous reaction at - 76.90 C delta G is negative. Threfore it is less than zero in the given reaction.
True statement
B. At - 76.90C conversion starts, therefore both phases don't coexist at - 76.9 c but after that temperature a coexistence of both phases do exist.
True statement
C. This most stable state depends on the temperature. Since (a) form is obtained at first when liquid freezes its to its crystalline form and then spontaneously cinverts to beta form at - 76.9 c. Accordingly beta form is more crystalline comparatively.
Even (- ve) temperature ×(-ve) sign in eq ; G=H-SdT statesthat (S) is more positive to beta state. Therefore it is more orderd.
False statement.
D. Since process is spontaneous heat evolves. It means that the reaction is exothermic. Therefore delta H is negative.
Statement false.
E. According to the conditions delta S seems to be positive.
Statement true.
F. Since spontaneityis obtained at 76.90 c, aftet that temperature only delta G is negative. Before that its positive and thats why conversion of states are ceased.
Statement false.
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