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CHM152GW7 S09 key

Chemistry (MasteringChemistry Series)

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CHM 152 Group Work 7 Crib 1. Predict whether the entropy change will be positive or negative for the following: a. H 2 O (g) J H 2 O (l) Δ S____ - __ b. C 6 H 12 O 6 (s) J 2C 2 H 5 OH(l) + 2CO 2 (g) Δ S__+__ c. 2NH 3 (g) + CO 2 (g) J H 2 O(l) + NH 2 CONH 2 (aq) Δ S_____-__ d. NaCl(s) J NaCl(aq) Δ S___+____ e. Cu(s) (100 o C) J Cu(s) (25 o C) Δ S_____-_ f. 2NH 3 (g) ' N 2 (g) + 3H 2 (g) Δ S___+____ 2. Calculate Δ H o rxn, Δ S o rxn and Δ G o rxn for 2 Mg(s) + O 2 (g) ' 2 MgO(s)) (Hint – balance the rxn) Δ H o rxn = [ 2(-601.7)] – [0] = -1203 kJ Δ S o rxn = [ 2(26.9)] – [ 1(32.7) + 1(205.0) ] = -216.6 J/K Δ G o rxn = [ 2(-569.4) ] – [0] = -1139 kJ 3. From # 2 the results for Δ H o rxn means ( exothermic or endothermic), the results for Δ S o rxn means (disorder or order ) increased, and Δ G o rxn means ( products or reactants) are favored under standard conditions. 4. Calculate K for MgCO 3 (s) ' MgO(s) + CO 2 (g) Δ G o rxn = [ -569.4 + -394.4 ] – [ -1012 ] = 48.2 kJ
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Unformatted text preview: Δ G o rxn = -RT lnK 48.2 kJ (1000J / kJ) = (-8.314 J/molK) (298 K) lnK lnK = -19.45 so K = 3.6 x 10-9 5. Calculate the temperature at which this reaction changes from being spontaneous to non spontaneous: Mg(s) + O 2 (g) ' MgO(s). Is the reaction spontaneous above or below this temperature? Set Δ G to zero to find the temp at which the rxn changes between spont and not spont 0 = Δ H- T Δ S 0 = (-1203 kJ) – T (-0.2166 kJ/K) T = -1203 kJ / -0.2166 kJ/K T = 5554 Kelvin or 5281 o C rxn is spont BELOW this temp 6. Calculate Δ G for Mg(s) + O 2 (g) ' MgO(s) at 30.5 o C if the pressure of oxygen gas is 1.33 atm. Δ G = Δ G o rxn + RT lnQ Δ G = (-1139 kJ) + (8.314 J/molK) (kJ / 1000J) (303.5 K) ln 1.33-1 Δ G = -1140 kJ = -1.140 x 10 3 kJ...
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