CHEE2325 – Lecture 5
Pure substances:
- A pure substance is one that has a fixed chemical composition throughout
(e.g., water, nitrogen, air, etc.).
- A mixture of two or more phases is still a pure substance as long as the
chemical composition of all phases is the same (e.g., a mixture of vapour and
liquid water, but not air and liquid air and air, as different components of air
condensate at different temperatures).
Phase changes:
- During a phase change, T is constant if P remains constant.
- The saturation temperature, T sat is the temperature at a given pressure at
which a pure substance changes phase.
- The saturation pressure, Psat is the pressure at a given temperature at which a
pure substance changes phase.
- The critical point of a substance is the point at which the saturated liquid and
saturated vapour diagrams are identical.
- The temperature and pressure at which these phase changes occur can be
represented with a P-V or T-V diagram.
Property tables:
- For most substances, the relationships among thermodynamic properties are
too complex to be expressed by equations. Therefore, properties are
presented in the form of tabulated data.
Saturated liquid-vapour mixture:
Pure substances:
- A pure substance is one that has a fixed chemical composition throughout
(e.g., water, nitrogen, air, etc.).
- A mixture of two or more phases is still a pure substance as long as the
chemical composition of all phases is the same (e.g., a mixture of vapour and
liquid water, but not air and liquid air and air, as different components of air
condensate at different temperatures).
Phase changes:
- During a phase change, T is constant if P remains constant.
- The saturation temperature, T sat is the temperature at a given pressure at
which a pure substance changes phase.
- The saturation pressure, Psat is the pressure at a given temperature at which a
pure substance changes phase.
- The critical point of a substance is the point at which the saturated liquid and
saturated vapour diagrams are identical.
- The temperature and pressure at which these phase changes occur can be
represented with a P-V or T-V diagram.
Property tables:
- For most substances, the relationships among thermodynamic properties are
too complex to be expressed by equations. Therefore, properties are
presented in the form of tabulated data.
Saturated liquid-vapour mixture:
