Physical Chemistry Chapter 2 CHAPTER 2 -. The First Law of Thermodynamics Basic Concepts Isothermal A system which is held at constant temperature Adiabatic: A system in which energy may be transferred as work but not as heat Diathermic: a system which allows energy to escape as heat through its boundary if there is a difference in temperature between the system and its surroundings5 Isothermal: A system which is held at constant temperature Adiabatic: A system in which energy may be transferred as work, but not as heat. CHAPTER 2 The First Law of Thermodynamics Basic Concepts Diathermic: A system which allows energy to escape as heat through its boundary if there is a difference in temperature between the system and its surroundings. Physical Chemistry Chapter 2