Assignment for Lab 14: Thermodynamics, Electrochemistry and Nuclear Chemistry La

Question

Assignment for Lab 14: Thermodynamics, Electrochemistry and Nuclear Chemistry Lab section: Name: Coosider the following reacion (balanced as written) and thermodynamie data from tables in your book: 3NO2(g) + H2O(l) 2HNOd) + NO(g) AHerkl/mol) 33.10 -285.8 174.1 90.29 S° (J/mol-K) 239.9 69.95 155.6 210.6 Substance a) What is the Gibbs free energy change for this reaction at 2s°c? b) What is the equilibrium constant for this reaction at 25°C? d) At 25'C his reaction is nonspontaneous. At what temperature would you expect this reaction to become spontaneous?

Explanation / Answer

Q1

a)

dG = dH - T*dS

dH = Hproducts - Hreactnants

dH = 2HNO3 + NO - (3NO2 + H2O)

dH = 2*-174.1 + 90.29 - (3*33.10 + -285.8)

dH = -71.41

dS =  2HNO3 + NO - (3NO2 + H2O)

dS = (2*155.6 + 210.6) - (3*239.9 + 69.95)

dS = -267.85 J/K = 0.26785 kJ/K

dG = (-71.41) - 298*(-0.26785)

dG = 8.3944 kJ/mol

b)

for K

dG = -RT*ln(K)

K = exp(-dG/(RT))

K = exp(-8394.4/(8.314*298))

K = 0.0337

c)

since K < 1, this is not spontaneous

there is favouring of reactants over products

for T

dG <0

then

dG = dH - T*DS < 0

dG = (-71.41) - T*(-0.26785) < 0

-71.41 < T*-0.26785

71.41 /0.26785 > T

266 K > T

T must be less than 266 K

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