| What does a born haber cycle show? | shows how ionic compounds are formed from their elements |
| equation for enthalpy of formation from born haber cycle? | atom + IE + EA + latt |
| what is AH latt? | AH when 1 mole of a solid ionic compound is separated into gaseous ions under standard conditions (endo)
NaCl (s) = Na+ (g) + Cl- (g) |
| what is AH atom? | AH when 1 mole of gaseous atoms is formed from an element in standard state (endo)
Na (S) = Na(g) |
| What is bond dissociation enthalpy? | AH when 1 mole of bonds is broken into gaseous state (endo)
Cl2 (g) = 2Cl (g) |
| What is AHf? | AH when 1 mole of a compound is formed from its elements in standard states under standard conditions (exo)
Na (s) + 1/2 Cl2 (g) = NaCl (s) |
| AH IE | energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms (Endo)
Na(g) = Na+(g) + E- |
| AH EA | AH when 1 mole of electrons are added to 1 mole of gaseous atoms (Exo)
Cl(g) +e- = Cl-(g) |
| AH sol formula | AH sol = AH atom + AH hyd |
| What are the factors that affect lattice enthalpy? (2) | 1) ion charge = higher charge means stronger attraction = bigger lattice enthalpy
Mg-2 O-2 > Na-Cl+
2) ionic radius = bigger radius decreases attraction = smaller lattice enthalpy
NaCl > KBr bec NaCl has a smaller radius = more attraction |
| what is AH sol? (4) | enthalpy change when 1 mole of ionic substance dissolves in water to give a solution of infinite dilution
NaCl (s) = Na+(aq) + Cl- (aq)
infinite dilution = excess water so adding more water wouldn't cause anymore heat to be released or absorbed
1) solid ionic compound is broken down into gaseous atoms (AH latt)
2) gaseous ions are hydrated with water AH hyd
= AH sol |
| What is AH hyd? (2) | when 1 mole of gaseous ions dissolves in water to give a solution of infinite dilution (exothermic)
Na+(g) = Na+ (Aq)
ion-dipole forces are formed bw gaseous ions and dipoles of water molecules |
| What does the AH sol of an ionic compound depend upon? | depends on how big latt is compared to hyd:
latt > hyd = endothermic sol
latt < hyd = exothermic sol |
| What is entropy? | measures the way the energy of a system is distributed among the particles (JK-1 mol-1)
higher entropy = positive
liquid = gas = higher entropy
AS = p - r |
| how to convert celsius to K? | +273 |
| Gibbs free energy change formula | AG = AH -TAS
only the temp value changes
T has to be in kelvin
and AS has to be divided by 1000 so it goes from J to KJ |
| definition of gibbs free change? | energy obtained from a chemical reaction that can do work |
| Reasons why entropy can increase? (5) | if number of moles increase (2 - 4)
if number of gas molecules increase
if temp increases
if pressure decreases
if there is no change in moles or number of gas molecules = entropy change is 0 |
| What is a spontaneous reaction? | one that happens without an outside influence
for a reaction to be spontaneous the AG of the reaction has to be negative |
| How to work out at what temp a reaction will be spontaneous? | make it equal to 0 and solve for T |
| How doe AS affect spontaneity? | positive = becomes more spontaneous as temp is increased
negative = less spontaneous as temp increases |
| How does AH and AS affect spontaneity? | - and + = spontaneous at all temps
+ and + = becomes more spontaneous as temp increases
- and - = becomes less spontaneous as temp increases
+ and - = never spontaneous |
| If the reaction is becoming more organised will the spontaneity be positive or negative? | negative bec less disorder |
| what happens when the no of moles and states of matter are the same? | very small change in entropy |
| AH formula? | r-p |
| Why will elements in its standard state be 0? | because it takes no energy to form a naturally occurring compound and is currently in its most stable form |
