The efficiency of a Carnot Engine is described by the relationship: Tc/Th = Qc/Qh, so that e(Carnot) = 1 - Tc/Th For heat engines, can their efficiency also be related to temperature as well? Or is the description of their efficiency just: e(heat engine) = W / Qh = 1 - Qc/Qh I am inclined to say that the only reason that a Carnot Engine's efficiency can be related to temperature like that, is because of the cyclic nature of the Carnot Cycle... But I'm not entirely sure. The reason I am asking this question, is because I am trying to understand how to solve the following problem: "A heat engine operating between 200C and 80C achieves 20% of the maximum possible efficiency. What energy input will enable the engine to perform 10kJ of work?" Tc/Th = Qc/Qh, W = Qh-Qc Therefore, Tc/Th = (Qh - W) / Qh --> Tc/Th = 1 - W/Qh So plugging in the above values, Qh = 16.7kJ My solution is only valid if I made the correct assumption that Carnot efficiency can be applied to a heat engine efficiency.