mmm.. just noticed that my other thread appear to not work for some reason.. anyhow, here is a resubmit: Problem: A heat engine is a decive that uses heat to perform work. the Carnot ideal heat engine runs through a cycle, which consists of a isothermal, adiabatic, again isothermal, and again adiabatic processes. The working substance (it can be an ideal gas) take heat QH from the hot reservoir with teh temperature TH and transfers a part of it Qc to the cold reservoir with the temperature Tc. During this cycle, the working substance expands and produces work W. The thermal efficiency e of the Carnot engine is the greatest one for the two definite temperatures of reservoirs: e = (TH-Tc)/TH = (QH-Qc)/QH = W/QH An ideal refrigerator or ideal heat pump is equivalent to a CArnot engine working in reverse. That is, energy Qc is taken in for a cold reservoir and energy QH is rejected toa hot reservoir. (An example of a non-ideal heat pump is an air conditioner) Find the work that must be supplied to run the ideal refrigerator with TH, Tc, and Qc given. The problem i'm having: Since this supposed to be a challange question, i thought my solution could be too simplistic.. After reading through the Carnot engine passage in the book, i don't think i fully understand it. However, after reading the question carefully again, i found out that the equation queston provides could be all that is nesscerry to solve this problem. Since they give me TH, Tc, i can find out e. Then, since they give me Qc, i can then find out QH from the second equation. Then, the work can be found using the third equation.. Could my approach work? Or is there something i'm missing here? Can any mod delete my other broken post please?