Q4. A refrigerator has a coefficient of performance of 4 and removes 500 J of heat from its inside. How much work does it need, and how much heat goes into the room?
W = Q2/α = 500/4 = 125 J. Heat into the room: Q1 = 500 + 125 = 625 J.
Q5. A gas expands isothermally and turns all the heat it takes in into work. Does this break the Kelvin–Planck statement?
No. Turning the heat into work is not the sole result: the gas also ends up at a larger volume and lower pressure. To repeat the process in a cycle and still get net work, the gas must be brought back while rejecting some heat to a colder body.
Q6. Can a kitchen be cooled by leaving the refrigerator door open? Explain.
No. The refrigerator gives out to the kitchen all the heat it removes from inside plus the electrical work it uses (Q1 = Q2 + W), so the kitchen as a whole gets warmer.