1. Calculate the change in the internal energy of the following systems and then

Question

1. Calculate the change in the internal energy of the following systems and then determine whether the processes are endothermic or exothermic: (a) 25 J of work is performed by the surroundings to the system.

Answer: E = ________________; the process is _______________________________.

(b) 500 J of heat is transferred from the surroundings to the system. Answer: E = ________________; the process is _______________________________.

(c) When 50 J of heat is transferred from the surroundings to the system, 150 J of work is done by the system to the surroundings. Answer: E = ________________; the process is _______________________________.

(d) An internal combustion engine performs 52 kJ of work to the surroundings and transfers 112 kJ of heat to the surroundings. Answer: E = ________________; the process is _______________________________.

(e) A 5.0 g sample of water is heated from 25 ºC to 35 ºC, thereby absorbing 8.4 kJ of heat from the surroundings. Answer: E = ________________; the process is _______________________________

Explanation / Answer

1. Calculate the change in the internal energy of the following systems and then determine whether the processes are endothermic or exothermic: (a) 25 J of work is performed by the surroundings to the system.

Answer: E = _____525 J___________; the process is ___________endothermic____________________.

(b) 500 J of heat is transferred from the surroundings to the system. Answer: E = ____525 J____________; the process is ________endothermic_______________________.

(c) When 50 J of heat is transferred from the surroundings to the system, 150 J of work is done by the system to the surroundings. Answer: E = _______-100_________; the process is _____exothermic__________________________.

(d) An internal combustion engine performs 52 kJ of work to the surroundings and transfers 112 kJ of heat to the surroundings. Answer: E = ____-60____________; the process is _____exothermic__________________________.

(e) A 5.0 g sample of water is heated from 25 ºC to 35 ºC, thereby absorbing 8.4 kJ of heat from the surroundings. Answer: E = _____8.38 kJ___________; the process is _____endothermic__________________________

solution for (e)

n = 5 / 18 = 0.278

H = E + n R dT

8.4 = E + 0.278 x 8.314 x 10^-3 x (35 -25)

E = 8.38 kJ

note :

for all problems only one formula

E = Q + W (work done on the system)

E = Q - W (work done by the system)

E = +ve endothermic

E = - ve exothermic

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