Based on the value of Q (the reaction quotient) when the solutions are first mix

Question

Based on the value of Q (the reaction quotient) when the solutions are first mixed, determine if precipitate will form when 0.20 L. of 6.2 times 10^-4 M Mg(NO_3)_2 is mixed with 0.10 L. of4.6 times 10^-4 M NaF. Include the correct expression for Q in your answer. (K_sp. of MgF_2 is 5.2 times 10^-11) Determine the change in entropy (deltas^0_sys) for the following reaction at 298 K. The standard molar entropies for the substance* are as follows: NOCI. S^0 = 264 J K-mol: NO. S^0 211 J/K-mol; Cl_2, S^0 = 223 J K-mol. 2NOCI(g) rightarrow 2NO(g) + CI_2(g) Calculate delta G^0_sys for a reaction at 298 K given that deltas^0_sys, equals +78.2 J K and deltaH^0_sys equals +126.0 kJ. Is the reaction spontaneous at that temperature?

Explanation / Answer

26. [Mg2+] = 6.2 x 10^-4 M x 0.2 L/0.3 L = 4.13 x 10^-4 M

[F-] = 4.6 x 10^-4 M x 0.1 L/0.3 L = 1.53 x 10^-4 M

Qsp = [Mg2+][F-]^2 = (4.13 x 10^-4)(1.53 x 10^-4)^2 = 9.67 x 10^-12

As, Qsp < Ksp, precipitate would not occur.

27. change in entropy

dSo(sys) = dSo(products) - dSo(reactants)

= (2 x 211 + 223) - (2 x 264)

= 117 J/mol-K

28. dGo(sys) = dHo(sys) - TdSo(sys)

= 126 - 298 x 0.0782

= 102.696 kJ/mol

the sign of dGo is +ve and thus the reaction is non-spontaneous.

Related Questions

Navigate

• Browse (All)
• Browse B
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.