ChemApp is a programmers library for thermochemistry, which allows the user to carry out a variety of calculations to simulate different process stages. It is a development of GTT Technologies, Herzogenrath, Germany. The software has been applied to a wide variety of problems, e.g. the sinter process for Fe-ores, the heat treatment of alloys, the cooling of waste gases, impurity and temperature distribution in a steel ladle, etc.

ChemApp is based on the local equilibrium concept that uses input streams of defined composition, temperature and pressure to obtain an equilibrium state for which either temperature and pressure or appropriate extensive property balances, e.g. enthalpy (heat), are given. From the equilibrium output, streams are generated which can be used in further process steps.