I saw a problem for which I don't really understand the idea of the solution. This is what it says: The vaporization latent heat for water (at 100 deg C) under normal pressure (101325 pa) is 2,3*10^6. What is the saturated vapor pressure for water at 105 deg C? And the solution says that we have to consider a Carnot cycle in which the isotherms are at 100 deg C and 105 deg C, and the adiabats transform the water from water to vapor and vice-versa. And so ,expressing the efficency for the Carnot cyle as W/Q=1-T1/T2, where T1=100 deg C and T2=105 deg C , and saying that Q=(Mass of vapour)* ( latent heat of vaporization) and W=(delta)p*(delta)V, where (delta) V is the volume of the vapour and approximately equat to (m*R*T2)/(molar mass of water) form the ideal gas law , we can obtain (delta)p ,and then the final pressure P final= (delta)p + p, where p is the normal atmospheric pressure. I am not stuck with the calcultion of this problem. I just don't understant why do we have to think of a Carnot cycle in a situation like this. When do we have to look at a system like at a Carnot cycle? Thank you!