The Internal Energy Calculator computes the change in internal energy (ΔU\Delta UΔU) using the First Law of Thermodynamics: ΔU=Q−W\Delta U = Q – WΔU=Q−W, where QQQ is the heat added to the system and WWW is the work done by the system. By entering any two of the three variables, the calculator determines the unknown. This tool is useful for thermodynamics students, laboratory experiments, and understanding energy changes in gases and chemical reactions.