Urea ((NH 2 ) 2 CO) can be formed from ammonia and carbon dioxide as shown in th

Question

Urea ((NH2)2CO) can be formed from ammonia and carbon dioxide as shown in the following reaction. The H° value for this synthesis is -134.0 kJ. Calculate the H°f for urea.
2NH3(g) + CO2(g) (NH2)2CO(s) + H2O(l)

Work backwards from the H° and the numerical data to derive the H°f of urea.   Someone answered this and said it was 453.12 kJ/mol but it turned out incorrect.

9. The S° value for urea the synthesis reaction above is -424.0 J/K. Calculate S° for urea.

10. Calculate G° for the synthesis of urea under standard conditions (298 K and 1 atm).

Work backwards from the H° and the numerical data to derive the H°f of urea.   Someone answered this and said it was 453.12 kJ/mol but it turned out incorrect.

Explanation / Answer

Q8

Hrxn = Hproducts - Hreactants

-134 = (-285.8 + H-urea ) -(2*-45.90 + -393.509)

solve for H-urea

H-urea = -134 + (2*-45.90 + -393.509) + 285.8 = -333.509 kJ/mol

Q9

dS = Sprod - Sreact = (Surea + 69.9) - (2*192.5 + 213.8) = -424

so

S-urea = -424 + (2*192.5 + 213.8) - 69.9 = 104.9 J/molK

Q10

dG = dH - T*dS = -333.509*10^3 - 298*104.9 = -364769.2J/mol = -364.77 kJ/mol

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