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Chapter 17
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Define key terms and concepts Explain the three laws of thermodynamics. Calculate the entropy for a system. Determine if a reaction is spontaneous or nonspontaneous. Calculate the Gibbs Free Energy for a reaction.
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Energy cannot be created or destroyed, only converted from one form to another. ΔH = ΔU + PΔV Δ H° rxn = ΣΔH° f(products) - ΣΔH° f(reactants)
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Spontaneous processes/reactions are favored over non- spontaneous processes. Entropy How dispersed the energy of a system is The more dispersed, the greater the entropy
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Solids have less entropy than liquids Liquids have less entropy than gases As a solute dissolves in solution, entropy increases. Where k = 1.38x10 -23 J/K W = the number of microstates S = k ln WΔS = S f - S i ΔS = k ln W f - k ln W i
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Melting aluminum Iodine crystals subliming A car accident Water freezing Dissolving sodium chloride in water
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The entropy of the universe increases in a spontaneous process and remains unchanged in an equilibrium process. For a spontaneous process, ΔS univ > 0 For an equilibrium process, ΔS univ = 0 ΔS univ = ΔS sys + ΔS surr
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For the general reaction: aA + bB cC + dD ΔS° rxn =[cS°(C) + dS°(D)] – [aS°(A) + bS°(B)] If the entropy for a system increases, ΔS° is positive. If the entropy for a system decreases, ΔS° is negative. ΔS° rxn = ΣnS°(products) - ΣnS°(reactants)
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If a reaction produces more gas molecules than it consumes, ∆S° is positive. If the total number of gas molecules diminishes, ∆S° is negative. If there is no net change in the total number of gas molecules, then ∆S° may be negative or positive, but the numerical value will be small.
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C 6 H 12 O 6(s) C 2 H 5 OH (l) + CO 2(g) NH 3(g) + CO 2(g) NH 2 CONH 2(aq) + H 2 O (l) CO (g) + H 2 O (g) CO 2(g) + H 2(g)
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Calculate the standard entropy of reaction for the following reaction at 25°C. C 6 H 12 O 6(s) C 2 H 5 OH (l) + CO 2(g)
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Calculate the standard entropy of reaction for the following reaction at 25°C. NH 3(g) + CO 2(g) NH 2 CONH 2(aq) + H 2 O (l)
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Calculate the standard entropy of reaction for the following reaction at 25°C. CO (g) + H 2 O (g) CO 2(g) + H 2(g)
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Surroundings System 1System 2 HeatHeat HeatHeat Entropy
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If the temperature of the surroundings is low, the energy released by a system will increase the entropy. The Third Law of Thermodynamics The Entropy of a perfect crystalline substance is zero at absolute zero temperature. ∆S surr = -∆H sys T
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The heat of vaporization, ∆H vap, of carbon tetrachloride at 25°C is 43.0 kJ/mole. If 1 mole of liquid carbon tetrachloride at 25°C has an entropy of 214 J/K, what is the entropy of 1 mole of the vapor in equilibrium with the liquid at this temperature?
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Liquid ethanol at 25°C has an entropy of 161 J/moleK. If the heat of vaporization, ∆H vap, at 25°C is 42.3kJ.mole, what is the entropy of the vapor in equilibrium with the liquid at 25°C?
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The energy available to do work. If ∆G<0, the reaction is spontaneous in the forward direction. If ∆G >0, the reaction is nonspontaneous in the forward direction. If ∆G=0, the system is at equilibrium and no net change in energy will be observed. ∆G= ∆H-T∆S
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Using ∆H° and ∆S° values from Appendix 3, calculate the ∆G° for the following reaction at 25°C. N 2(g) + H 2(g) NH 3(g)
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Using ∆H° and ∆S° values from Appendix 3, calculate the ∆G° for the following reaction at 25°C. CaCO 3(s) ↔ CaO (s) + CO 2(g)
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Using ∆H° and ∆S° values from Appendix 3, calculate the ∆G° for the following reaction at 25°C. KClO 3(s) ↔ KCl (aq) + O 2(g)
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∆H∆S∆G ++ Reaction is spontaneous in the forward direction at high temperatures, but is spontaneous in the reverse direction at low temperatures. +-∆G is always positive. Non-spontaneous reaction. -+∆G is always negative. Spontaneous reaction. -- Reaction is spontaneous in the forward direction at low temperatures, but is spontaneous in the reverse direction at high temperatures.
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Standard Free Energy of a Reaction (∆G° rxn ) The change in free energy when 1 mole of a compound is synthesized from its elements in their standard state. For the general reaction: aA + bB cC + dD ΔS° rxn =[cS°(C) + dS°(D)] – [aS°(A) + bS°(B)] ΔG° rxn = ΣnG° f (products) - ΣnG° f (reactants)
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Determine if the following reaction is spontaneous using Gibbs Free Energy if the reaction is conducted at 25°C. CaCO 3(s) CaO (s) + CO 2(g)
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Determine if the following reaction is spontaneous using Gibbs Free Energy if the reaction is conducted at 25°C. KClO 3(s) KCl (aq) + O 2(g)
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Determine if the following reaction is spontaneous using Gibbs Free Energy if the reaction is conducted at 25°C. NH 3(g) + CO 2(g) NH 2 CONH 2(aq) + H 2 O (l)
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For calculating reactions where not all reactants and products are in their standard states. Where R= 8.314 J/Kmole T is temperature in Kelvin K is the equilibrium constant. ΔG° = -RTlnK
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KInKΔG°Affect at Equilibrium > 1+-Products are favored = 100Neither side of the reaction is favored < 1-+Reactants are favored
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What is the value of the equilibrium constant K at 25°C for the following reaction? Predict whether the products or reactants are favored at equilibrium. CaCO 3(s) ↔ CaO (s) + CO 2(g)
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What is the value of the equilibrium constant K at 25°C for the following reaction? Predict whether the products or reactants are favored at equilibrium. KClO 3(s) ↔ KCl (aq) + O 2(g)
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What is the value of ΔG° at 25°C for the following reaction? The K sp of magnesium hydroxide is 1.8x10 -11. Predict whether the products or reactants are favored at equilibrium. Mg(OH) 2(s) ↔ Mg 2+ (aq) + OH - (aq)
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What is the value of the equilibrium constant K at 25°C for the following reaction? The K sp of lead (II) iodide is 6.5x10 -9. Predict whether the products or reactants are favored at equilibrium. PbI 2(s) ↔ Pb 2+ (aq) + I 2 - (aq)
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