chamber is monitored either using a thermometer or thermocouple, and the temperature plotted against time to give a graph from which fundamental quantities can be calculated. Modern calorimeters are frequently supplied with automatic devices to provide a quick read-out of information, one example being the differential scanning calorimeter. Systems Several thermodynamic definitions are very useful in thermochemistry. A system is the specific portion of the universe that is being studied. Everything outside the system is considered the surroundings or environment. A system may be: a (completely) isolated system which can exchange neither energy nor matter with the surroundings, such as an insulated bomb calorimeter a thermally isolated system which can exchange mechanical work but not heat or matter, such as an insulated closed piston or balloon a mechanically isolated system which can exchange heat but not mechanical work or matter, such as an uninsulated bomb calorimeter a closed system which can exchange energy but not matter, such as an uninsulated closed piston or balloon an open system which it can exchange both matter and energy with the surroundings, such as a pot of boiling water Processes A system undergoes a process when one or more of its properties changes. A process relates to the change of state. An isothermal (same-temperature) process occurs when temperature of the system remains constant. An isobaric (same-pressure) process occurs when the pressure of the system remains constant. A process is adiabatic when no heat exchange occurs. See also Differential scanning calorimetry Important publications in thermochemistry Isodesmic reaction Principle of maximum work Reaction Calorimeter Thomsen-Berthelot principle Julius Thomsen Thermodynamic databases for pure substances Calorimetry Photoelectron photoion coincidence spectroscopy Thermodynamics Cryochemistry Chemical kinetics References External links Physical chemistry Branches of thermodynamics