2. Thermodynamic Properties of a Pure Substance

# 2.5 Chapter review

An important step in thermodynamic analysis is to predict the thermodynamic properties, in particular, the intensive properties at different states of a process or a cycle. In this chapter, we have introduced common thermodynamic properties of pure substances, and how to use phase diagrams and thermodynamic tables to determine the phase of a fluid and its corresponding properties at a given state. Below are the key takeaways:

- Pure substances may be used as working fluids in thermal devices. A pure substance may exist as a single-phase matter, such as solid, liquid, vapour or gas, or a saturated two-phase mixture.
- The state of a pure substance can be illustrated in the [latex]P-T, \, T-v,[/latex] and [latex]P-v[/latex] phase diagrams.
- A state of a pure substance is fixed by
**two independent, intensive properties**.- For a single-phase fluid, if two intensive properties from the list: [latex]T, P, v, u, h,[/latex] and [latex]s[/latex] are known, then the state is fixed.

- For a two-phase mixture, if two properties from the list: [latex]T, P, v, u, h, s[/latex] and the quality [latex]x[/latex] are known, then the state is fixed.

- For a single-phase fluid, if two intensive properties from the list: [latex]T, P, v, u, h,[/latex] and [latex]s[/latex] are known, then the state is fixed.
- The properties of a fixed state can be extracted from the thermodynamic tables directly or by using linear interpolations.
- [latex]P-T, \,T-v,[/latex] and [latex]P-v[/latex] diagrams are of particular importance in thermodynamic analysis. It is highly recommended that students relate the appropriate phase diagrams to the flow charts in Section 2.4, when practicing how to locate a state and how to read thermodynamic tables.