Thermo Lecture 6 Flashcards
Define ‘Equation of State’
An equation showing the relationship between the values of the pressure, volume, and temperature of a quantity of a particular substance.
When is the ideal gas law most appropriate?
Low pressures (around 1 bar) and high temperatures (above the supercritical temperature)
Give the equation for the compressibility factor Z. What is it for?
Z = PV/RT
Use to look at how gases deviate from the ideal. It is indicative of the intermolecular forces. (Z<1 implies attractive forces, Z>1 implies repulsive forces)
Give Van der Waals EOS (Dont need to remember)
(P + a/V^2)(V-b) = RT
What is the problem with the Van der Waals EOS? What do we do to overcome this?
Below Tc are 3 solutions to the equation at a given P. Cubic function shows an increase in V for an increase in P which doesn’t make sense in reality.
Do a Maxwell Construction where you replace the cubic curve with a straight line.
How do we find a critical compressibility factor?
Normalise P, V and T using critical values (i.e Pr = P/Pc) and use these values to calculate Z.
What are the 2 types of EOS?
Empirical and Fundamentally Based EOSs
What us an Empirical EOS?
One that takes the ideal gas EOS as the starting point and adds fitting parameters e.g. Redlich-Kwong
What is a Fundamentally Based EOSs?
One that is derived from a theoretical basis and considers molecular interactions as a starting point. e.g. Virial EOS
What must EOS for solids include?
A consideration for material properties
What is magma?
An assemblage of melt, suspended solids and dissolved volatiles
Define liquidus
The temperature above which a material is completely liquid
Define solidus
The temperature at which melting begins
What is the ‘Eutectic point’?
The lowest temperature at which liquid is present
