Different systems in a thermodynamics

Thermodynamics: Types of Systems and Entropy

Three different thermodynamic systems are under study. Their analysis is given below:

(a) Type of system in Case 1

Case 1: Water is boiling in an open container with continuous supply of heat.

Type of system: Open system

Reason: An open system allows exchange of both matter and energy with surroundings. Heat enters the system continuously and water vapour escapes from the container.

(b) Case in which entropy increases continuously

Answer: Case 1

During boiling, liquid water changes into vapour. Continuous heat supply and phase change increase molecular randomness, hence entropy increases continuously.

(c) Expression for internal energy change in Case 1

For an open system, internal energy change is given by:

dU = δQ − δW + Σh_indm_in − Σh_outdm_out

Where δQ is heat supplied, δW is work done, h is enthalpy and dm represents mass flow.

(d) System in which entropy decreases with time

Answer: Case 3

In freezing, liquid changes into solid. Molecular motion decreases and order increases, therefore entropy decreases with time.

Summary Table

Case	Type of System	Entropy Change
Case 1 (Boiling, open)	Open system	Increases continuously
Case 2 (Boiled water, closed)	Closed system	Nearly constant
Case 3 (Freezing, closed)	Closed system	Decreases