59 PROBLEMS (1 Latm 101325J, 1 L bar 100.000 J) 1. In an exothermie process, the

Question

59 PROBLEMS (1 Latm 101325J, 1 L bar 100.000 J) 1. In an exothermie process, the volume of a system contracted from 3243 ml. to 2087 mL against a constant pressure of 1.o63 bar. During the process, 124. was the internal energy change for the system in joules? 6 calories of heat energy were released. What 2. Calculate the change in internal energy for the thermal decomposition of 5-432 g of potassium chlorate at a constant external pressure of 1.634 bar. The decomposition reaction is Potassium chlorate's heat of formation is -391.20 kl/mol, potassium chloride's heat of formation is 43587 kJ/mol, and oxygen has a density of 1.308 g/Lat the reaction temperature. Recall that the enthalpy of a reaction can be determined by a summation of enthalpies of formation.

Explanation / Answer

Q1

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Q - W = dU

substitute known data

P = 1.063 bar = 106300Pa

W = -P(Vf-Vi) = -106300*(2087-3242)*10^-6 = -122.7765 J

negative, since it is being compressed

Q = 124.6 cal --> 124.6*4.184 = -521.3264 J

negative, since released

so

dU = Q - W = -521.3264 - -122.7765 J

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