Consider a closed thermodynamic system that can exchange energy with its surroundings only in the form of heat or work. Answer the following questions related to the conventions used in the First Law of Thermodynamics.
(i) Define heat, work and internal energy for a thermodynamic system.
(ii) State the algebraic sign convention for heat and work adopted in classical thermodynamics and explain its physical meaning with one example for each sign.
(iii) Using the above conventions, justify why the First Law is written in the form ΔU=Q−W for a finite process between two equilibrium states.