The phase diagram for a pure chemical substance is given below. The locations of

Question

The phase diagram for a pure chemical substance is given below. The locations of the three points labeled a, b, and c are also given. a) What is the normal melting point for the substance (pressure and temperature)? b) Which phase has a higher density - the solid phase, or the liquid phase? Justify your answer (no credit unless both the correct and a correct justification). c) What is the value for delta H degree_vap, the enthalpy of vaporization for the substance? d) Is there enough information given to find delta H degree_fus. the enthalpy of fusion for the substance? If your answer is yes, find the value for delta_H degree_fus. If your answer is no, indicate the additional information that would be needed to find delta H degree_fus.

Explanation / Answer

A) the normal boiling point is at pressure 1 atm at what temperature liquid turns to vapor.

From graph it is point c T = 372.4 K

(b)

Solid phase has more density the volume is very less in solid phase so for same mass density should be higher for solid.

(C)

Enthalpy of vaporization can be found by classius equation.

Ln(P2/P1) = - delta H /R ( 1/T2 - 1/T1)

Take points (a) and (c) from graph.

ln(1/0.36) = - delta H/R ( 1/372.4 - 1/308.7)

Delta H/ R = 1843.78

Delta H = 1843 .78 * 8.314 =15330 J/mol

(D) similarly if you find for points (a) and (b) you get delta H fusion.

Finally delta sublimation = delta vapor + delta fusion

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