# Lecture 25 - 3/15/10 The internal energy of a system...

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3/15/10 1 12 The internal energy of a system increases by 26 J while 69 J of heat is transferred from the surroundings to the system. Calculate the work, and specify whether it is done by the system or by the surroundings. A) +43 J, done by surroundings B) –43 J, done by system C) +95 J, done by surroundings D) –95 J, done by system ! E system = q + w Work done by the system on surroundings w = ! E system " q = +26 J " (+69 J) Energy of system increases System absorbs heat = " 43 J 13 q rxn = " 16.7 kJ q calorimeter = " q rxn When 0.00295 moles of sucrose are burned in a bomb calorimeter, the temperature rises from 24.92 °C to 28.33 °C. Find q rxn. The energy of an isolated system is constant ( ! E isolated system = 0) (different sign: one absorbs, other releases) w = 0 q calorimeter = C calorimeter (T f – T i ) C calorimeter = 4.90 kJ/°C (experimentally determined) q calorimeter = 4.90 kJ/°C(28.33°C – 24.92°C) = 16.7 kJ heat released Negative q rxn EXOTHERMIC 4.1.B. Pressure-volume (PV) work The most common type of work encountered in chemical processes is either: Work = w = F # ! h pressure (P) = force (F) / area (A) w = P # A #! h w = " P ! V Units of work? J (joules) 14 work done by a gas (expansion ; w < 0) work done to

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## This note was uploaded on 04/22/2010 for the course CHEM 102 taught by Professor Brown during the Winter '10 term at University of Alabama at Birmingham.

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Lecture 25 - 3/15/10 The internal energy of a system...

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