10-29-090 - Today: Today: Enthalpies of Reaction are useful...

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Today: Today: Enthalpies of Reaction are useful Can be calculated for any reaction
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Last time : H 2 ( g ) + ½ O 2 ( g ) H 2 O ( g ) H = - 241.8 kJ You calculated that 13.4 kJ are released for the synthesis of 1g of water. exothermic C 8 H 18 ( l ) + 12 ½ O 2 ( g ) 8 CO 2 ( g ) + 9 H 2 O ( g ) Now : H = - 5461 kJ
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C 8 H 18 ( l ) + 12 ½ O 2 ( g ) 8 CO 2 ( g ) + 9 H 2 O ( g ) H = - 5461 kJ
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C 8 H 18 ( l ) + 12 ½ O 2 ( g ) 8 CO 2 ( g ) + 9 H 2 O ( g ) H = - 5461 kJ How much energy is released by the combustion of 3mL of C 8 H 18 ? Note: Density = 0.688 g/mL Molecular weight = 114 g/mol Answer: - 98.9 kJ
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1g of water: * To warm it up by 1 degree: C = 4.184 x 10 -3 kJ * To convert it into steam (at 100˚): H v = 2.3 kJ * To “break” it: H = 13.4 kJ Reminder: So 98.9 kJ should be noisier than last time…
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Where did the 98.9 kJ go? Work Heat Sound C 8 H 18 ( l ) + 12 ½ O 2 ( g ) 8 CO 2 ( g ) + 9 H 2 O ( g ) H = - 5461 kJ Enthalpy change for the combustion of isooctane:
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State Functions State Functions E and H are “state” functions. Their value depends only on the state the system is in, not on the path it took to get there. Work and Heat are not “state” functions. Their values depend on the path taken.
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Altitude is a state function.   Altitude is a state function.   Distance is not. Distance is not.
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Recall once again… Recall once again… Energy diagrams, and activation energy Exothermic process: reactants products E a H < 0
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CH 4 ( g ) + 2O 2 ( g ) CO 2 ( g ) + 2H 2 O( g ) H 2 O( l ) H 2 O( g ) Simplify Diagram to Just Relative 
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This note was uploaded on 12/18/2009 for the course BIOL 101 taught by Professor Wormer during the Fall '08 term at Purdue University-West Lafayette.

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10-29-090 - Today: Today: Enthalpies of Reaction are useful...

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