Open Question
What is the standard Gibbs free energy for the transformation of diamond to graphite at 298 K?
19. Chemical Thermodynamics
Entropy Calculations
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Calculate ΔS°rxn for the reaction: 2NO(g) + O2(g) → 2NO2(g) given the standard molar entropies: S°(NO) = 210.7 J/mol·K, S°(O2) = 205.0 J/mol·K, S°(NO2) = 240.1 J/mol·K.
A
-146.3 J/mol·K
B
-73.15 J/mol·K
C
146.3 J/mol·K
D
73.15 J/mol·K
Verified step by step guidance1
Understand that the change in standard entropy for a reaction, ΔS°rxn, is calculated using the formula: ΔS°rxn = ΣS°(products) - ΣS°(reactants).
Identify the standard molar entropies given in the problem: S°(NO) = 210.7 J/mol·K, S°(O2) = 205.0 J/mol·K, S°(NO2) = 240.1 J/mol·K.
Calculate the total entropy of the products. Since there are 2 moles of NO2 produced, multiply the standard molar entropy of NO2 by 2: 2 × S°(NO2).
Calculate the total entropy of the reactants. For NO, there are 2 moles, so multiply the standard molar entropy of NO by 2: 2 × S°(NO). Add the entropy of O2: S°(O2).
Subtract the total entropy of the reactants from the total entropy of the products to find ΔS°rxn: ΔS°rxn = [2 × S°(NO2)] - [2 × S°(NO) + S°(O2)].
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