Question

Effciency of a heat engine cannot be 100 %even if the system is ideal and frictionless​

Answer 1

Answer:

The second law of thermodynamics puts a fundamental limit on thethermal efficiency of all heat engines. Even an ideal, frictionless engine can't convert anywhere near 100% of its input heat into work. ... No device converting heat into mechanical energy, regardless of its construction, can exceed this efficiency

Answer 2

heat engines are never 100% efficient. It would mean that the energy input equals to the energy output and there is no losses in the system. Such an ideal situation could only happen is if the system was in an absolute vacuum environment. ... This means the engine is only around 20% efficient.