4. Calculate the standard entropy change for: N 2 (g) + 3 H 2 (g) ® 2 NH 3 (g) a

Question

4. Calculate the standard entropy change for: N2 (g) + 3 H2 (g) ® 2 NH3 (g) at 298 K.

                                    S° (J/molK)

N2 (g)                         210

H2 (g)                         190

NH3 (g)                      240

5. The boiling point of water occurs at 100°C. The heat of vaporization for water is

40,700 J/mol. Calculate the entropy change for the phase change of water from liquid to gas.

6. Use the given thermodynamic data to determine the equilibrium constant for the reaction at 25°C:

N2 (g) + O2 (g) ® 2 NO (g)

DG° (kJ/mol)

N2 (g)                         0

O2 (g)                         0

NO (g)                       55

7. Magnesium hydroxide, Mg(OH)2, has a pH of 8.50 Find the Ksp of magnesium hydroxide.

Explanation / Answer

Ans 4

Entropy change of reaction = sum of Entropy of formation of products - sum of Entropy of formation of reactants

S = 2*Sf(NH3) - 3*Sf(H2) - Sf(N2)

= 2*240 - 3*190 - 210

= - 300 J/mol·K

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