23. Which statement is corect at 25°C and i atm pressure? (A) AGf for Hg() 0kJmo

Question

23. Which statement is corect at 25°C and i atm pressure? (A) AGf for Hg() 0kJmol (B) r, for 12(g) = 0 kJ.mor1 (C) Nr, for H2O(I) = 0 kJmol-1 (D) S° for O2(g)=0/mor'K" 24. The boiling point of chloroform, CHC, is 61.78C and its enthalpy of vaporization is 31.4 kJ mor1. Calculate the molar entropy of vaporization for chloroform (A) 10.7 J-mol-1K-1 (B) 93.8 J-mol K-1 (D) 509 J-mol K- (C) 301 J-mot K- 25. Which of the following processes are spontaneous? X. 2 H2O(/) 2 H2(g) + O2(g) at 298 K Y. H2O(/) H2O(g) at 374 K and 1.0 atm Z. formation of a solution when sodium chloride and water are mixed at 298 K A. Y and Z only B. none of them C. X and Y only D. all of them 26. N,(g) + 20,(g) 2NO2(g) AHrs? 0 Under what temperature conditions is this reaction spontaneous at standard pressure? (A) at low temperatures only

Explanation / Answer

23)

enthalpy change for element in their standard state at STP is 0

standard state of Hg is liquid

standard state of I2 is solid

H2O is not an element

So is entropy

1st one is correct

Answer: A

24)

delta H = 31.4 KJ/mol

= 31400 J/mol

T = 61.7 oC

= (61.7 + 273) oC

= 334.7 K

use:

delta S = delta H / T

= 31400 J/mol / 334.7 K

= 93.8 J/mol.K

Answer: B

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