thermodynamics my own notes

Enthalpy change

Heat energy change measures under conditions of constant pressure

Rules of Born Haber cycle (when calculating)

All different (against flow)=right flow (with the flow)

When writing equations for dissolving ionic compound in water, what should you not do

Don’t include water, just the ionic compound breaking up

Enthalpy of solution equation and what to remember

Lattice dissociation enthalpy + (sum of hydration enthalpies of all ions), so if have enthalpy of solution, must change the sign of lattice dissociation enthalpy

Why would an ion have a less exothermic value or enthalpy of hydration (compared to other ions)

Has a less exothermic value when had a larger ionic radius so has a lower charge to size ratio, so has a weaker attraction to water molecules

What state has the highest entropy and why

Gases because they are more disordered than solids

At what temperature is entropy 0

0K

Equation for free Gibbs energy

DeltaG = deltaH - TdeltaS

What is the minimum temp for feasibility

DeltaH = 0

When calculating calculations involving Gibbs free energy what must you remember to do

Convert deltaS

Delta H=

Products - reactants

DeltaS=

Products - reactants

When is a reaction feasible (Gibbs free energy)

When deltaG<0

What helps feasibility and when

When deltas is positive, increasing temperature helps feasibility

If in a Born Haber cycle the gas is diatonic what must you do

Multiply their enthalpies by 2

Lattice enthalpies become more exothermic when

Ionic charge is higher, ionic radius is smaller, charge density is higher

To decide on charge density with lattice enthalpies what to do

Use charge product rule

Why does the enthalpy of hydration become less exothermic down group 1

Because going down the group, the ion gets bigger, and larger ions attract water molecules less readily so will be less exothermic, so the attraction between the metal ions and the negative partial charge on the oxygen of the water molecule decreases

What do the state symbols depend on in Born Haber cycles

The definition and the element (for example, iodine is a solid in its standard state)

Standard enthalpy of solution

The enthalpy change when 1 mole of a compound is formed from its elements in their standard states

Standard state of F2

Gas

Standard state of Cl2

Gas

Standard state of Br2

Liquid (l)

Standard state of I2

Solid

Standard state of all metals

Solid

Standard state of H2

Gas

Standard state of O2

Gas

Standard state of N2

Gas

Standard state of C

Solid (graphite)

Standard state of P4

Solid (white phosphorus)

Standard state of S8

Solid

For what types of enthalpies do you divide the value by 2

Bond dissociation (not lattice), atomisation of X2 (not X)