Phase equilibrium & solutions

Question 1

Phase: definition

Answer 1

a part of a system that is homogeneous in chemical and physical state throughout and is separated from other phases by a definite boundary.

Question 2

How does increasing the temperature affect the kinetic energy of the molecules?

Answer 2

Increasing the temp, increases the amount of kinetic energy the molecules have

Question 3

Vapour pressure: definition

Answer 3

The pressure of a vapour when it is in equilibrium with its condensed phase.

Question 4

saturated vapour pressure: definition:

Answer 4

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.

Question 5

relationship between temp and vapour pressure

Answer 5

higher temperatures = higher vapour pressures.

Question 6

difference between gas and vapour

Answer 6

gas: substances that are gases at room temperature.
vapour: describes the gas phase that are solid or liquid at room temperature.

Question 7

phase diagrams: definition

Answer 7

used to show the effect of these properties on the phase – can be single or multi-component systems.

Question 8

phase boundaries: definition

Answer 8

lines on a phase diagram – represent the conditions where phase changes take place and 2 phases are in equilibrium.

Question 9

critical point: definition

Answer 9

the end-point of a phase equilibrium curve.

Question 10

critical temperature: definition

Answer 10

the temperature at and above the point where the vapour of the substance cannot be liquified.

Question 11

critical pressure: definition:

Answer 11

the vapour pressure of a fluid at the critical temperature above which distinct liquid and gas phases do not exist

Question 12

Intermolecular forces: definition

Answer 12

all attractive and repulsive forces that exist between molecules and atoms that don’t include covalent chemical bonds.

Question 13

Properties influenced by intermolecular forces:

Answer 13

Melting and boiling points.

Viscosity.

Surface tension.

Cohesion

Adhesion

Question 14

What is cohesion and adhesion?

Answer 14

Cohesion: attraction of molecules to each other.

Adhesion: attraction of molecules to a surface.

Question 15

What are Intramolecular bonds:

Answer 15

chemical bonds, e.g. covalent or metallic.

Question 16

What is the permittivity of a vacuum?

Answer 16

describes how the potential energy acts through the medium separating the charges.

Question 17

What is ε(0)?

Answer 17

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

Question 18

permittivity of a medium equation?

Answer 18

ε = ε(r) ε(0)

Question 19

What are non-covalent interactions:

Answer 19

interactions between molecules that have no overall charge.

Question 20

When do dipole-dipole interactions occur?

Answer 20

between molecules that have no formal charge but have a permanent dipole moment.

Question 21

relationship between the size of the dipole moment and strength of the interaction?

Answer 21

the larger the dipole moment – the stronger the interaction.

Question 22

What is a dipole moment? What is its symbol? Units?

Answer 22

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.

Question 23

What occurs in a Dipole-induced dipole interaction?

Answer 23

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.

Question 24

What does the strength of the induced dipole depend on?

Answer 24

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.

Question 25

What are dispersion forces?

Answer 25

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.

Question 26

Other names for induced dipole – induced dipole interactions:

Answer 26

dispersion forces or London interactions.

Question 27

What is polarizability?

Answer 27

the degree to which the electron cloud is influenced by an electric field.

Question 28

relationship between the polarizability and the dipole:

Answer 28

higher the value of the polarizability, the more easily the electrons can be distorted by a nearby dipole or charge