The thermodynamic Brayton cycle with a reversible chemical reaction

A Brayton cycle is considered in which the working substance is a chemically reacting gas with molar weight and heat capacity changing as a result of a reversible chemical reaction. By way of example, the reaction N$_{2}$+3H$_{2}\leftrightarrow$ 2NH$_{3}$ is considered. For a constant heat supply, the cycle is characterized by the lower ($T_{low}$) and upper ($T_{top}$) temperature boundaries of existence; between these boundaries, the efficiency can change from 0 to 1. Such peculiar properties are manifested because of two factors: reversibility of the chemical reaction and the special role of the chemical work in the conversion of heat into mechanical work, which minimizes the heat loss to the surrounding space in a closed thermodynamic cycle.