(1) Calculate the G°rxn using the following information. 2HNO3(aq) + NO(g) 3 NO2

Question

(1) Calculate the G°rxn using the following information. 2HNO3(aq) + NO(g) 3 NO2(g) + H2O(l)

H°f (kJ/mol) -207.0 91.3 33.2 -285.8

S°(J/molK) 46.0 210.8 240.1 70.0 G°rxn = ?

(2) Above what temperature does the following reaction become nonspontaneous?

FeO(s) + CO(g) CO2(g) + Fe(s) H= -11.0 kJ; S = -17.4 J/K

(3) Which of the following is NOT true for Grxn?

(e) If Q = 1, then Grxn = G°rxn.

4. Use standard entropies to calculate Srxn for the balanced chemical equation:

2PCl3(l)+O2(g)2POCl3(l)

5. Determine G°rxn using the following information.

H2(g) + CO(g) CH2O(g) H°= +1.9 kJ; S°= -109.6 J/K

(a) If G°rxn > 0, the reaction is spontaneous in the forward direction. (b)If G°rxn > 0, the reaction is spontaneous in the reverse direction. (c)If G°rxn = 0, the reaction is spontaneous in the reverse direction. (d)Under equilibrium conditions, Grxn = 0.

(e) If Q = 1, then Grxn = G°rxn.

4. Use standard entropies to calculate Srxn for the balanced chemical equation:

2PCl3(l)+O2(g)2POCl3(l)

Substance S (J/mol K) POCl3(l) 222.5 POCl3(g) 325.5 PCl3(l) 217.1 PCl3(g) 311.8 O2(g) 205.2

Explanation / Answer

(1) Calculate the G°rxn using the following information. 2HNO3(aq) + NO(g) 3 NO2(g) + H2O(l)

Given: H°f (kJ/mol) -207.0 91.3 33.2 -285.8 ... S°(J/molK) 46.0 210.8 240.1 70.0 G°rxn = ?

Apply

dG = dH - T*dS

We will need both,

dH= Hproducts - Hreacants= 3*NO2 + H2O - (2HNO3 + NO) = 3*33.2+ 285.8 - (2*-207.0 + 91.3 ) = 708.1 kJ/mol

for dS:

dS = Sproducts- Sreactants = 3*NO2 + H2O - (2HNO3 + NO) = 3*240.1 + 70.0 - (2*46.0 + 210.8 ) = 487.5 J/molK

change to kJ/molK --> 487.5 J/molK = 0.4875 kJ/molK

Substitute

dG = dH - T*dS

dG = 708.1 kJ/mol - 298 K *0.4875 kJ/molK

dG = 562.825 kJ/mol

(2) Above what temperature does the following reaction become nonspontaneous?

FeO(s) + CO(g) CO2(g) + Fe(s) H= -11.0 kJ; S = -17.4 J/K

Apply free energy criteria, if dG < 0, then this is spontaneous

dG = dH - T*dS < 0

dH - T*dS <0

dH/dS < T

(-11.0)/(-17.4 /1000) < T

632.18 < T

T must be greater than 632.18K

(3) Which of the following is NOT true for Grxn?

(a) If G°rxn > 0, the reaction is spontaneous in the forward direction. FALSE, the entropy of universe decreases in this case, s it violate 2nd law of thermodynamics

(b)If G°rxn > 0, the reaction is spontaneous in the reverse direction. True, if we invert the process, this is likely to occur

(c)If G°rxn = 0, the reaction is spontaneous in the reverse direction. False, this must be in equilibrium

(d)Under equilibrium conditions, Grxn = 0. True, for any reaction

(e) If Q = 1, then Grxn = G°rxn. True, since dG = dG° + RT*ln(Q) by definition, if Q = 1, then ln(1) = 0, so dG = dG°

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