Write and simplify the closed-system energy balance (Equation 7.3-4) for each of the following processes, and state whether nonzero heat and work terms are positive or negative. Begin by defining the system. The solution of Part (a) is given as an illustration.

(a) The contents of a closed flask are heated from 25°C to 80°C.

(b) A tray filled with water at 20°C is put into a freezer. The water turns into ice at - 5°C. When a substance expands it does work on its surroundings and when it contracts the surroundings do work on it.

(c) A chemical reaction takes place in a closed adiabatic (perfectly insulated) rigid container.

(d) Repeat Part (c), only suppose that the reactor is isothermal rather than adiabatic and that when the reaction was carried out adiabatically, the temperature in the reactor increased.