1. Basic Concepts Flashcards
What is a system ?
A part of the Universe containing matter and energy that is separated from its surroundings by an arbitrarily imposed boundary.
Define surroundings
The rest of the Universe.
Matter and energy are transferred from the system to the surroundings
Open system
What is exchanged between the system and surroundings in an isolated system ?
No mass and no energy is transferred (in theory, in reality energy will still be transferred)
What is exchanged between the system and the surroundings in a closed system ?
Only energy (no matter is transferred)
What is a property ?
A macroscopic characteristic of a system which can be measured at a given time without knowledge of the previous behaviour of the system (e.g. pressure and temperature)
To describe a system and predict its behaviour we need knowledge of what ?
Properties of the system and how those properties are related.
Define state
The condition of a system as described by its thermodynamic properties or state variables
Two groups of thermodynamic properties ?
Extensive and intensive
What is an extensive property ?
A property that depends on the amount of substance or size of the sample.
Examples: mass, volume
(These properties are additive)
What is an intensive property ?
A property that is independent of the size or extent of the system, and may vary from place to place within the system at any moment
Examples: density, temperature
(These properties are not additive)
Define substance
The material performing the energy transformation
Especially includes working fluid
Examples of working fluids
Liquid, vapour and gas are working fluids.
Important working fluids: water/steam & ideal gases (air)
What is a pure substance ?
A pure substance is homogeneous and invariable in chemical composition.
(E.g. a) water + ice = pure subs. b) liquid air + air = not pure subs.)
Define phase
A physically homogenous aggregation of a substance
E.g. Solid, liquid or gas
