This preview shows page 1. Sign up to view the full content.
Unformatted text preview: phase of a substance can be approximated by the relation ln(P) = 21.38804 – 3776.53 / T and that of the vapor pressure of the solid phase of that substance by ln(P) = 27.42117 – 4834.93 / T. In both cases, T is given in kelvin and P in kPa. Estimate the standard enthalpy of fusion for this substance. Show your calculations. a) 40. kJ/mol b) 34 kJ/mol c) 61 kJ/mol d) 29 kJ/mol e) 8.8 kJ/mol f) 8.6 kJ/mol g) 2.3 kJ/mol h) 5.7 kJ/mol i) 6.1 kJ/mol j) 9.5 kJ/mol k) 11 kJ/mol l) 14 kJ/mol We know from the expression of the pressure of the vapor phase in equilibrium with the liquid, that ΔvapH / R = 3776.53. From this we conclude that ΔvapH = 31.4 kJ/mol Similarly, ΔsubH / R = 4834.93, from which we conclude that ΔsubH = 40.2 kJ/mol We also know that ΔfusH + ΔvapH = ΔsubH Hence, ΔfusH = 8.8 kJ/mol 4 Question 15: (5 points) The temperature dependence of the vapor pressure of the liquid phase of a substance can be approximated by the relation ln(P) = 21.38804 – 3776.53 / T and that of the vapor pressure of the solid phase of that substance by ln(P) = 27.42117 – 4834.93 / T. In both cases, T is given in kelvin and P in kPa.  9
What is the triple point pressure for this substance? (Should be in the range 10 kPa to 100 kPa.)  3
a) 1.7 kPa b) 1.2x10 kPa c) 0.87 kPa d) 3.1 kPa e) 0.24 kPa f) 8.6 kPa  7
g) 6.1 kPa h) 5.7 kPa i) 1.6x10 kPa j) 9.5 kPa k) 1.3 kPa l) 14 kpa Show your derivations and calculations. The triple point is a state, which is described by the intersection of the three coexistence curves (S/L, S/V and L/V). Solving the above two equations with two u...
View
Full
Document
This note was uploaded on 01/26/2014 for the course CHEM 3615 taught by Professor Aresker during the Spring '07 term at Virginia Tech.
 Spring '07
 AREsker
 Physical chemistry, pH

Click to edit the document details