Phase equilibrium & solutions Flashcards
Phase: definition
a part of a system that is homogeneous in chemical and physical state throughout and is separated from other phases by a definite boundary.
How does increasing the temperature affect the kinetic energy of the molecules?
Increasing the temp, increases the amount of kinetic energy the molecules have
Vapour pressure: definition
The pressure of a vapour when it is in equilibrium with its condensed phase.
saturated vapour pressure: definition:
if the container is closed and temperature is constant, the vapour and liquid comes to an equilibrium – the equilibrium and vapour pressure is called the saturated vapour pressure.
relationship between temp and vapour pressure
higher temperatures = higher vapour pressures.
difference between gas and vapour
gas: substances that are gases at room temperature.
vapour: describes the gas phase that are solid or liquid at room temperature.
phase diagrams: definition
used to show the effect of these properties on the phase – can be single or multi-component systems.
phase boundaries: definition
lines on a phase diagram – represent the conditions where phase changes take place and 2 phases are in equilibrium.
critical point: definition
the end-point of a phase equilibrium curve.
critical temperature: definition
the temperature at and above the point where the vapour of the substance cannot be liquified.
critical pressure: definition:
the vapour pressure of a fluid at the critical temperature above which distinct liquid and gas phases do not exist
Intermolecular forces: definition
all attractive and repulsive forces that exist between molecules and atoms that don’t include covalent chemical bonds.
Properties influenced by intermolecular forces:
Melting and boiling points.
Viscosity.
Surface tension.
Cohesion
Adhesion
What is cohesion and adhesion?
Cohesion: attraction of molecules to each other.
Adhesion: attraction of molecules to a surface.
What are Intramolecular bonds:
chemical bonds, e.g. covalent or metallic.
What is the permittivity of a vacuum?
describes how the potential energy acts through the medium separating the charges.
What is ε(0)?
a constant used to describe the system if the two charges are separated by a vacuum and has a value of 8.854 x 10 ^-12 J / C^2 / m
permittivity of a medium equation?
ε = ε(r) ε(0)
What are non-covalent interactions:
interactions between molecules that have no overall charge.
When do dipole-dipole interactions occur?
between molecules that have no formal charge but have a permanent dipole moment.
relationship between the size of the dipole moment and strength of the interaction?
the larger the dipole moment – the stronger the interaction.
What is a dipole moment? What is its symbol? Units?
many neutral molecules contain dipoles which arise from the uneven distribution of electronic charge within the molecule – the strength of this molecule is measured by the dipole moment
given the symbol: μ.
SI unit for μ = C m (coulomb metres) - gives small values so the Debye, D, is often used. 1 D = 3.3356 x 10^-30 C m.
What occurs in a Dipole-induced dipole interaction?
when a molecule with a dipole, approaches a molecule without one, it induces the movement of electrons causing a temporary dipole in the non-polar molecule, so there is an attractive interaction.
What does the strength of the induced dipole depend on?
strength of the induced dipole depends on how easily the electron cloud of the non-polar molecule can be moved around - measured by the polarizability of the molecule, α, the higher the value of α, the more easily the electrons can be distorted by a nearby dipole or charge.
What are dispersion forces?
when non-polar species can have an instantaneous dipole due to time dependent changes in electron density.
this then induces a dipole on an adjacent species resulting in an electrostatic interaction.
Other names for induced dipole – induced dipole interactions:
dispersion forces or London interactions.
What is polarizability?
the degree to which the electron cloud is influenced by an electric field.
relationship between the polarizability and the dipole:
higher the value of the polarizability, the more easily the electrons can be distorted by a nearby dipole or charge
