Section 2 - Properties of Pure Substances Flashcards
What’s a pure substance?
A substance that has fixed chemical composition throughout.
A mixture of various chemical compounds may also qualify as a pure substance, so long as it remains homogenous (air).
Can a pure substance exist in more than one phase?
Yes, same chemical composition but different physical structures (liquid, solids, gases).
What is a compressed (subcooled) liquid?
A liquid that is not about to vaporise.
From internet: A fluid under thermodynamic or mechanical conditions that force it to be a liquid.
What does the term ‘sensible energy’ mean?
We can measure the energy change by some parameter.
What is a ‘saturated liquid-vapour mixture’?
Liquid and vapour phases coexist in equilibrium.
Give the properties of ‘Superheated Vapour’.
Increase the temperature of the fluid and the fluid will expand.
Decrease the temperature and the fluid will contract with no condensation taking place.
Explain the relationship between saturation temperature and saturation pressure.
Explain what do those two terms mean.
The temperature at which a liquid start boiling depends on the pressure; therefore is the pressure is fixed, so is the boiling temperature.
Saturation temperature – At a given pressure, the temperature at which a pure substance changes phase.
Saturation pressure – At a given temperature, the pressure at which a pure substance changes phase.
Give the definition of latent heat.
Latent heat is the amount of energy absorbed or released during a phase change.
What’s the difference between latent heat of fusion and vaporisation?
Amount of heat:
Latent heat of fusion … absorbed during melting
Latent heat of vaporisation … released during condensation.
Define another meaning for a system in terms of liquids and vapours.
A system contains a mixture of saturated liquid and saturated vapour at T and p.
What is the dryness or quality fraction?
The ratio of the mass of vapour to the total mass of the mixture (only for the states within the saturation dome).
What’s a superheated vapour?
- It’s a single phase region
- Temperature and pressure are no longer dependent and so they can be used to fix a state.
What is a saturated liquid?
A liquid that is about to vaporise.
What is the equation of state?
Any equation that relates the pressure, temperature, and specific volume of a substance.
What’s an incompressible substance?
A substance whose specific volume (or density) is constant.
