Conversion of chemical energy into mechanical work is the fundamental mechanism of several natural phenomena at the nanoscale, like molecular machines and Brownian motors. Quantum mechanical effects are relevant for optimizing these processes and to implement them at the atomic scale. This paper focuses on engines that transform chemical work into mechanical work through energy and particle exchanges with thermal sources at different chemical potentials. Irreversibility is introduced by modeling the engine transformations with finite-time dynamics generated by a time-dependent quantum master equation. Quantum degenerate gases provide maximum efficiency for reversible engines, whereas the classical limit implies small efficiency. For irreversible engines, both the output power and the efficiency at maximum power are much larger in the quantum regime than in the classical limit. The analysis of ideal homogeneous gases grasps the impact of quantum statistics on the above performances, which are expected to persist in the presence of interactions and more general trapping. The performance dependence on different types of Bose-Einstein condensates (BECs) is also studied. The BECs under consideration are standard BECs with a finite fraction of particles in the ground state, and generalized BECs where eigenstates with parallel momenta, or those with coplanar momenta, are macroscopically occupied according to the confinement anisotropy. Quantum gases are therefore a resource for enhanced performances of converting chemical into mechanical work.
