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 _______________________________

Answer 1

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