One mole of either carbon monoxide or benzene are completely combusted with oxyg

Question

One mole of either carbon monoxide or benzene are completely combusted with oxygen at constant temperature and pressure (298 K and 1 atm) to generate CO_2 and H_2O. Assume all substances are ideal gases for calculating volume changes. a. Write out balanced combustion reactions for each reaction. b. Calculate the change in entropy for the system for each reaction, using the table, below. c. Use the enthalpies of formation to calculate the heat lost or gained during this reaction. d. Use your result in part c) to calculate the change in entropy of the surroundings for each reaction. e. Also calculate Delta U, Delta A, Delta G for the system for each reaction. f. Which of the four thermodynamic potentials (Delta U, Delta H, Delta A, Delta G) is suited for an experiment at constant T, P when evaluating if the reaction is spontaneous? What if the experiment is conducted in a rigid container at constant temperature?

Explanation / Answer

a.

CO + 1/2O2 = CO2

C6H6 + 15/2O2 = 6CO2 + 3H2O

b.

dS-CO = CO2 - (CO - 1/2*O2)

dS-CO = 213.7- (197.7- 1/2*205.1) = 118.55 J/molK

dS-C6H6= (6CO2 + 3*H2O) - (C6H6 - 15/2*O2)

dS-C6H6= (6*213.7 + 3*188.8) - (269.3- 15/2*205.1) = 3117.55 J/molK

c.

dH-CO = CO2 - (CO - 1/2*O2)

dH-CO = -393.5- (-110.5- 1/2*0) = -283 kJ/mol

dH-C6H6= (6CO2 + 3*H2O) - (C6H6 - 15/2*O2)

dH-C6H6= (6*-393.5+ 3*-241.8) - (82.9- 15/2*0) = -3169.3 J/molK

d.

For CO:

dS surr = Q/T = -dH/T = -3117.55 *1000/298 = -10461.577 J/molK

For C6H6

dS surr = Q/T = -dH/T = --3169.3 *1000/298 = -10635.234 J/molK

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