test 1

entropy

measure of disorder of a system J mol^-1 K^-1

entropy increase

• with t

• solid → liquid → (greater) gas

• perfect crystals at 0 K = 0

• big increase on state changes

total entropy change

entropy change of the system

• +ve → increase in entropy - favourable

• -ve → decrease in entropy

entropy change of the surroundings

feasibility of a reaction

possibility that reaction will occur spontaneously

feasibility depends on

• balance between S [system] and S [surroundings]

• t (higher t decrease magnitude of S [surroundings], so its contribution to S [total] is less)

reaction is thermodynamically feasibility if

S [total] is + ve

exo or endo more favourable

exo

why S [system] -ve

• moles decrease

• decrease in disorder

why high Ea

• bonding/electrostatic attraction is strong

or

• large amount of energy needed to break bonds in …

ionisation

• 1 mole of gaseous atoms loses e^-

• 1st and 2nd endo

electron affinity

• 1 mole of gaseous atoms gains e^-

• 1st - exo, 2nd - endo

enthalpy of atomisation

• 1 mole of gaseous atoms produced

• from element in standard state

• endo

hydration enthalpy

• 1 mole of gaseous ions is hydrated (dissolved)

• …(g) + aq → …(aq)

• exo

enthalpy of solution

• 1 mole of an ionic solid dissolves so that ions are separated

• …(s) + aq → …(aq) + …(aq)

bond dissociation enthalpy

• 1 mole of covalent bonds is broken

• in gaseous state

• …₂ (g) → 2…(g)

• endo

lattice enthalpy of formation

• 1 mole of ionic solid is formed

• from ions in gaseous state

• …(g) + …(g) → …(s)

• exo

lattice enthalpy of dissociation

• 1 mole of ionic solid is broken up

• into ions in gaseous state

• …(s) → …(g) + …(g)

• endo

enthalpy of vaporisation

• 1 mole of liquid turned into gas

• exo

enthalpy of fusion

• 1 mole of solid turned into liquid

• endo

Born-Haber cycle

1. formation ↓

2. atomisation ↑

3. ionisation (1st, 2nd) ↑

4. e^- affinity (1st, 2nd) ↑

5. lattice enthalpy of formation ↓

does the sign of S [system] make sense

• disorder increases/decreases

• as no. of molecules/moles increases/decreases

advantages and disadvantages of using t higher than … in Haber process

• rate of reaction is higher

• more … produced in given time

• at higher t S [surr] is less +ve (decreases)

• S [total] more -ve

• Kp decreases

• eq position moves further right/left

effect of charge and size of ion on lattice energy

• (compound) more exo

• (ion) larger than (ion)

• charges on ions are the same

• (ion) forms stronger attractions

is atm or Pa bigger

atm

rate determining step

all reactants from rate equation have to be in this step or made in steps before

why k for the reaction is higher at higher t

• more particles have E > Ea

• rate is higher

ionic compound w most covalent character

• caton - high charge and small radius

• anon - large radius

why experimental value of lattice energy more exo than theoretical

why … only slightly soluble

• S [sys] is large and positive

• S [total] is positive

• S [total] = Ssurr + Ssys

how to find equilibrium constant using S [total]

e affinity of Cl VS I

Cl

• more exothermic

• as Cl ion is smaller

• stronger attraction/ more electronegative

when you have 2 constants

expression for K