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Ch.17 - Chemical ThermodynamicsWorksheetSee all chapters

Entropy Calculations

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Spontaneous vs Nonspontaneous Reactions
Entropy
Entropy Calculations
Entropy Calculations: Phase Changes
Third Law of Thermodynamics
Gibbs Free Energy
Gibbs Free Energy Calculations
Gibbs Free Energy And Equilibrium

Calculations dealing with entropy take into account the effects of our chemical reaction and its surroundings.

Entropy Calculations & Theory

Concept #1: The Total Entropy change of the Universe takes into account the contributions of the chemical reaction and its surroundings.

Example #1: Calculate the total entropy change for a reaction with ∆Ssurr = 2.7 J/K and ∆Sºrxn = - 450.0 kJ/K.

Is this reaction spontaneous?

Concept #2: The entropy of the surroundings is based on the enthalpy of your reaction and its temperature

Example #2: Determine change in entropy of the universe for the following reaction at 32ºC.

2 A (g) + 5 B (s) → AB (g) + 2 C (g) ∆Hrxn = -140 kJ , ∆Srxn = 3.6 J/K

Concept #3: Like enthalpy, the entropy of a chemical reaction can be calculated from standard molar values.

Example #3: Calculate ∆Sºrxn for the following reaction at 25ºC.

2 NO (g) + O2 (g) → 2 NO2 (g) ∆Hrxn = -114.14 kJ

Practice: For the following reaction at 27 °C, calculate ∆S°rxn, ∆Ssurr, and ∆Stot. Determine if reaction is favorable.

Fe2O3 (s) + 3 H2 (g) → 2 Fe (s) + 3 H2O (g) ∆Hrxn = 98.8 kJ