Question

a. Explain the operation of thermodynamic systems i.e. open system and closed system with the aid of diagrams and examples.

b. Define the term 'property of a substance' in a thermodynamic system and state the main difference between intensive and extensive properties with examples.

Answer 1

Basic information-- 1. System-- A system is a part of universe which is being studied.

2. Surrounding--- Surrounding the the part of universe which is outside of the system. The system is subjeced to the surrounding factors such as temperature, pressure, humidity etc.

3. Boundary-- A boundary is something which seperates system from surrounding.

Please look at the pic for more clearity.

A system can interact in two ways with the surrounding 1. Mass interaction and 2. Energy interaction.

Also note that energy interaction is also of two types 1. Work interaction and 2. Heat interaction.

A. OPEN SYSTEM-- Open system allows the exchange of energy and mass across its boundary.

Example-- human body is an open system, a pot with boiling water without a lid is also an open system, nozzle, turbine, compressor etc.

B.CLOSED SYSTEM-- Closed system allows the energy transfer but not the mass transfer across its boundary.

Example- pressure cooker, a pot with boiling water with a lid( because vapour can not go into surrounding).

B. 1. PROPERTY OF A SUBSTANCE-- Properties are the characterstics of a system which define the physical condition or state of a system.

Properties are the state variables of the system. Pressure, temperature, volume, mass etc are the properties. By defining them we are explaining its physical condition or state.

Also note that properties are the macroscopic characterstics of a system and they do not depend on the past history of the system.

2. Difference between intensive and extensive properties--

The major difference between the two is that intensive properties depend on the mass and extensive properties do not depend on the mass.

For example density is the intensive property. If we take 1kg iron aur 3 kg iron the density of iron will be same in both the case. Other intensive properties are melting/boiling point, pressure, specific heat capacity, specific volume, viscosity, conductivity, coefficent co thermal expansion etc.

Now, volume/ energy/moles/ entropy .Are the extensive properties they will vary if we take 1 kg in place of 3 kg mass. Other extensive properties are gibbs energy, enthalpy, heat capacity, internal energy etc.