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Thermodynamics

Thermodynamics. By: Mickie Andrews & Michelle Myszka. Definitions. Thermodynamics The study of energy in a reaction, and why the reaction occurs. Spontaneity Whether a process occurs without any outside help, and is spontaneous. Entropy (S) A measure of randomness or disorder.

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Thermodynamics

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  1. Thermodynamics By: Mickie Andrews & Michelle Myszka

  2. Definitions • Thermodynamics • The study of energy in a reaction, and why the reaction occurs. • Spontaneity • Whether a process occurs without any outside help, and is spontaneous. • Entropy (S) • A measure of randomness or disorder. • Is measured in J/K.

  3. Equations • ∆G˚ = ∆H˚- T∆S˚ • ∆ S˚ Reaction = ΣS˚ products - ΣS˚ reactants • ∆G˚ = ∆G˚ f, products - ∆G˚ f,reactants • ∆G˚ = -RTlnK • ∆G = -nFE

  4. Predicting Change in Entropy • Water evaporating: H2O(l) → H2O(g) Positive • Decomposition of Calcium Carbonate: CaCO3 (s) → CaO (s) + CO2(g) Positive • Na(s) + ½ Cl2 (g) → NaCl(s) Negative • 1 mol of N2 gas is expanded from 23.41 L to 100L Positive

  5. Calculating ∆S Predict the sign of ∆S˚ and then calculate the ∆S˚. 2 SO3(g) → 2 SO2 (g) + O2 (g) • ∆S values: • SO2 (g) : 248 • O2 (g) : 205 • 2 SO3(g) : 257 • Answers: • Positive ∆S, with a value of 187 J/K.

  6. Multiple Choice #1 • For which of the following processes would ∆S have a negative value? • I. 2 Fe2O3(s) → 4 Fe (s) + 3 O2 (g) • II. Mg2+ + 2 OH- → Mg(OH)2(s) • III. H2 (g) + C2H4 (g) → C2H6 (g) • A) I only • B) I and II only • C) I and III only • D) II and III only • E) I, II, and III

  7. Multiple Choice #2 N2 (g) + 3 H2(g) → 2 NH3(g) The reaction indicated above is thermodynamically spontaneous at 298 K, but becomes non-spontaneous at higher temperatures. Which of the following is true at 298 K? • A) ∆G, ∆H, ∆S are all positive • B) ∆G, ∆H, ∆S are all negative • C) ∆G and ∆H are negative, but ∆S is positive • D) ∆G and ∆S are negative, but ∆H is positive • E) ∆G and ∆H are positive, but ∆S is negative

  8. Multiple Choice #3 • Chose the reaction that is expected to have the greatest increase in entropy. • A) H2O(g) → H2O(l) • B) C(s) + O2 (g) → CO2(g) • C) Ca(s) + H2(g) → CaH2 (s) • D) N2 (g) + 3 H2(g) → 2 NH3(g) • E) 2 KClO3(s) → 2 KCl (s) + 3 02 (g)

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