gammon win08 quiz1 - Show work or state logic get units and...

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Chemistry 152 A Winter 2007 Quiz # 1 – Answer Key Possibly useful information: 1 atm = 101 KPascal; R = 8.2 J/ o K/mol; PV = nRT; ΔΕ = Q + W; H = E + PV; W = - P ex Δ V; ΔΗ = Qp; 1 L atm = 101 J. 1) Energy and enthalpy, 6 points. A balloon, containing a fixed mass of a monoatomic ideal gas, is expanding its volume as heat is absorbed at an external pressure of 1 atm. Assume that ONLY “PV” work against the atmosphere is involved, in addition to the added heat. The balloon + the gas it contains is “the system.” Everything else is “the surroundings.” At the point where the volume of the balloon has increased by Δ V = 8L, answer the following if Δ E sys is then also measured to be 100 J: a)What is W sys ? Show work or state logic, get units and sign “right!” W sys = - P Δ V = - (1 atm) . (8 L) . 101 J/ atm L = - 808 J O r W sys = - P Δ V = - (1 atm . 101x10 -3 Pa/atm) . (8 L . 10 -3 m 3 /L) = - 808 J W sys = - 808 J b)What is Q surroundings
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Unformatted text preview: ? Show work or state logic, get units and sign “right!” Δ E sys = Q sys + W sys So, Q sys = Δ E sys - W sys = (100 J) – (- 808 J) = 908 J Q surroundings = - Q sys = - (908 J) = - 908 J Q surroundings = - 908 J c) What is ΔΗ sys ? Show work or state logic, get units and sign “right!” ΔΗ sys = Qp sys = 908 J O r ΔΗ sys = E + P Δ V = 100 J + 808 J = 908 J ΔΗ sys = 908 J 2) Heats of reaction & Hess’s Law (4 points). Given the data: Fe(solid) + ½ O 2 (gas) Æ FeO(solid) ΔΗ = -272 kJ/mol 2FeO(solid) + ½ O 2 (gas) Æ Fe 2 O 3 (solid) ΔΗ = -282 kJ/mol Determine ΔΗ for the reaction: 2 Fe(solid) + 3/2 O 2 (gas) Æ Fe 2 O 3 (solid) 2 Fe(solid) + O 2 (gas) Æ 2 FeO(solid) ΔΗ = 2 X (-272 kJ/mol) 2FeO(solid) + ½ O 2 (gas) Æ Fe 2 O 3 (solid) ΔΗ = -282 kJ/mol 2 Fe(solid) + 3/2 O 2 (gas) Æ Fe 2 O 3 (solid) ΔΗ = [2 X (-272 kJ/mol)]+-282 kJ/mol ΔΗ = -826 kJ/mol...
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This note was uploaded on 04/10/2008 for the course CHEM 152 taught by Professor Chiu during the Winter '08 term at University of Washington.

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gammon win08 quiz1 - Show work or state logic get units and...

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