BeginnerTopic 3 of 105Thermodynamics & Fluids
Properties and state
Pressure, temperature, volume and others define the state of a substance.
In depth
Properties are measurable characteristics (T, P, V, U, H, S). Intensive properties do not depend on mass (T, P, density), extensive do (V, U). Two independent intensive properties fix the state of a simple compressible pure substance (state postulate).
Key points
- Specific properties = extensive/mass
- Path-independent
- Equilibrium states only
ExampleWater at 1 bar and 100 °C could be liquid or vapour; quality is needed as a second property.
What is Properties and state?
Pressure, temperature, volume and others define the state of a substance.
Why is it important to understand properties and state?
Properties define the state of a substance, so once you know a few of them, all others follow from tables or equations.
What is a state point?
A set of property values that completely describes the substance at one moment, such as pressure and temperature for a single-phase fluid.
How many properties define a simple compressible substance?
Two independent intensive properties, such as pressure and temperature, define its equilibrium state.
How is Properties and state used in practice?
Typical applications include looking up the specific volume of steam at a known pressure and temperature, checking the state of a refrigerant in a cycle and describing the conditions in a tyre using pressure and temperature.
What should I learn before Properties and state?
Study "Open, closed and isolated systems" first (topic 2 of 105 in Thermodynamics & Fluids). It covers the groundwork this topic builds on.
What are the key points of Properties and state?
Specific properties = extensive/mass. Path-independent. Equilibrium states only.
Can you give an example of Properties and state?
Water at 1 bar and 100 °C could be liquid or vapour; quality is needed as a second property.
What comes after Properties and state?
The next topic is "Temperature and zeroth law", which builds directly on this one.
How difficult is Properties and state?
It is classed as Beginner in Thermodynamics & Fluids (topic 3 of 105). It is an entry-level topic. It relies only on basic school mathematics and the ideas introduced earlier in this discipline.