phase equilibria

exothermic phase changes

condensing and freezing

explain equilibrium including pressure for boiling point

X (l) ⇌ X (g) - increasing T shifts this eqm to the right

at the boiling point, T_b, vapour pressure (partial pressure) is equal to the pressure of the surroundings. below this, some of the substance is still in the gas phase but eqm lies to the left.

normal boiling point

pressure = 1 atmosphere

standard boiling point

pressure = 1 bar

define system and surroundings for entropy

system is where experiment is carried out, eg beaker, anything outside this is the surroundings and the universe if the system and surroundings combined

open system

matter and energy can be transferred

closed system

matter cannot be transferred but energy can

isolated system

neither energy nor matter can be transferred

adiabatic boundary

thermal energy cannot be exchanged between the system and surroundings

diathermal boundary

thermal energy can move freely between the system and surroundings

what is entropy and its symbol

entropy, S, is a measure of the distribution of energy

system and surroundings equation

change in entropy from solid → liquid → gas

increase in translational and rotational freedom

ΔS = +ve

can enthalpy and entropy be measured directly

entropy yes, enthalpy no

equation for entropy change of the system

do you multiply by the stoichiometry

yes

how can ΔS_surr be found

calculate from

system and surroundings equation rearrangement without ΔS_surr

gibbs free energy equation

when is a process spontaneous

when ΔG < 0

ΔG for solid, liquid and gas transitions

from solid to liquid to gas, ΔS and ΔH are both positive

at low T, ΔH > TΔS and ΔG is positive

at high T, ΔH < TΔS and ΔG is negative

table for positive and negative ΔH and ΔS

what is trouton’s rule

exceptions?

many substances have a similar entropy of vaporisation (ΔS^⦵vap ≈ 85 JK^-1mol^-1)

substances with strong H bonding

strong H bonding in the liquid phase

S_liquid is lower than expected and S_gas is similar to expected so ΔS is higher

strong H bonding in the gas phase

hydration of a cation

hydration of an anion