Question

A domestic refrigerator is loaded with food and the door closed. During a certain period the machine consumes 1 kW h of energy and the internal energy of the system drops by 5000 kJ. Find the net heat transfer for the system. (Hint: 1 W = 1 J/s & 1 kW = 1000 W

Answer 1

Given:

change in energy (ΔE) = 5000 kJ

electrical work = 1 kW h

To Find:

the net heat transfer for the system(q) =?

Solution:

Now, we know that electrical work = 1 kW h (negative sign since consumes)

on converting it in kJ ( 1 kW h = 3600 kJ)

W =  -3600 kJ (negative sign since consumes)

also, it is given

ΔE = -5000 kJ  (negative sign since drops)

from the first law of thermodynamics, we know that

q = ΔE + W

q = -5000 - 3600 = -8600 kJ

Thus, the net heat transfer for the system(q) = -8600 kJ

Answer 2

Answer:

Above solution seems to be correct