230_Sp10_L08_post-1

230_Sp10_L08_post-1 - CHEM 230 Sp10 Lecture 08 Chapter 6...

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CHEM 230 Sp10 Lecture 08 Chapter 6: Calculate Δ H from knowns 1) Hess’ Law 2) Δ H o 3) Bond enthalpy Session ID: 230

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Problem A calorimeter with heat capacity equivalent to 0.739 grams of water is used to measure the heat of combustion of 0.303 g of sucrose (C 12 H 22 O 11 MW = 342 g/mol). The temperature increase was found to be 5.00 o C. Calculate the heat that would be released by this reaction C 12 H 22 O 11 (s) + 12 O 2(g) 12 CO 2(g) + 11H 2 O (g) q rxn = -q Cal = -mC H2O Δ T = -0.739g (4.184 J )(+5.00 o C) g o C = -15.46 J C s,H2O = 4.184 J/g o C
The energy calculate is it the energy for the combustion reaction as written? C 12 H 22 O 11 (s) + 12 O 2(g) 12 CO 2(g) + 11 H 2 O (g) Δ H rxn =? " 15.5 J 0.303 g sucrose * 342 g sucrose 1 mol sucrose = " 17400 J 1 mol sucrose Δ H rxn =

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Thermochemical Equations C (s, graphite) + O 2(g) ˠ CO 2(g) Δ H = -393.509 kJ 2C (s, graphite) + 2O 2(g) ˠ 2CO 2(g) Δ H = -787.018 kJ (*2) 4C (s, graphite) + 4O 2(g) ˠ 4CO 2(g) Δ H = -1574.04 kJ (*4) CO 2(g) ˠ C (s, graphite) + O 2(g) Δ H = 393.509 kJ (reversed; change sign) Which are exothermic, which endothermic?
Assuming gasoline and diesel engines consume the same number of moles of fuel, and lose the same amount of heat to the surroundings, which fuel would give you more work per mol combusted? Δ comb (gasoline) = -6160 kJ/mol Δ comb (diesel) = -7940 kJ/mol A) Gasoline B) Diesel C) They would be equal D) There is insufficient information to say Concept Question

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Assuming gasoline and diesel engines consume the same number of moles of fuel, and lose the same amount of heat to the surroundings, which fuel would give you more work per mole combusted? Δ
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This note was uploaded on 01/24/2012 for the course PCHEM 230 taught by Professor Gottfried during the Fall '11 term at University of Michigan.

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230_Sp10_L08_post-1 - CHEM 230 Sp10 Lecture 08 Chapter 6...

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