Abstract
The Brighton cycle is considered, where a chemically reacting gas is used as a working substance and its molar weight and heat capacity change because of a reversible chemical reaction. The lower T_low characterizes a cycle with a constant heat supply and upper T_top temperature limits of existence, between these limits the thermal efficiency can vary from 0 to 1. Such unusual properties are manifested due to two factors: the reversibility of the chemical reaction and the special role of chemical work in the transformation heat into mechanical work.