It is a science of energy transfer and its effect on the properties of a system.
A system is a region containing energy and/or matter that is separated from its surroundings by arbitrarily imposed walls or boundaries. In a thermodynamic analysis, the system is the subject of the investigation.
Everything external to the system is the surroundings.
A boundary is a closed surface surrounding a system through which energy and mass may enter or leave the system.
- No mass transfer to or from the system or the surrounding.
- Energy may transfer to or from the system or the surrounding
E.g. Piston cylinder arrangement, without valves gas in a closed container.
- Mass and energy both may transfer to or from the system or the surrounding.
E.g. Compressor, Turbine etc.
Isolated system (Special case of Closed system)
An isolated system is a thermodynamic system that cannot exchange either energy or matter outside the boundaries of the system. There are two ways in which this may occur:
- The system may be so distant from another system that it cannot interact with them.
- The system may be enclosed such that neither energy nor mass may enter or exit.
An extensive property is a property that depends on the amount of matter in a sample. The mass of an object is a measure of the amount of matter that an object contains.
An intensive property is a property of matter that depends only on the type of matter in a sample and not on the amount.
Example: colour, temperature, density, and solubility.
- A process is said to be a reversible process if when reversed follows the same path without leaving any effect on the system and surroundings.
- The quasi-static process is called a reversible process
- All reversible processes can be shown on diagrams. Ex. P–V, T–S, P–T diagrams
- A process is said to be an irreversible process if when reversed follows a different path, leaving an effect on the system & surroundings.
- All spontaneous processes are irreversible processes.
- The irreversible process cannot be shown on diagrams. They are shown as dotted lines.
Example: Heat transfer to finite temperature difference, Free expansion.
A system will be in a state of thermodynamic equilibrium if the condition for the following three types of equilibrium is satisfied.
(i) Mechanical equilibrium
The net force on a system should be 0, i.e. all the forces should be balanced.
(ii) Chemical equilibrium
All the chemical reactions occurring inside a system should cease after reaching an equilibrium state.
(iii) Thermal equilibrium
There should be no heat transfer between the system and surroundings.