chapter 22: entalphy and entropy

What does lattice enthalpy mean?

The formation of one mole of an iconic solid from its gaseous ions

What is the sign for lattice entalphy of formation?

Negative because oppositively charged gaseous ions attract each other and form a stable lattice causing energy to be released

What effects lattice entalphy?

• ionic charge- more negative/positive the more the attraction

• Ionic radius- smaller the greater the attraction

Entalphy change of atomisation

Formation of 1 mol of gaseous atoms from an element in its standard state

Entalphy change of formation?

Formation of 1 mol of a compound from its element in their standard state

What are the two steps when an ionic solid dissolves?

The lattice breaks apart and the ions are hydrated

Entalphy change of solution?

The entalphy change when 1 mol of ionic compound is fully dissolved in water

NaCl(s) → Na⁺(aq) + Cl⁻(aq)

Entalphy of lattice of formation for sodium chloride

Na⁺(g) + Cl⁻(g) → NaCl(s)

Entalphy change of hydration?

when 1 mol of gaseous ions fully dissolve in water eg

Na⁺(g) → Na⁺(aq)

Cl⁻(g) → Cl⁻(aq)

What is the symbol of entropy?

S

What is entropy?

The measure of the dispersal of energy in a system

How to calculate entropy?

Products - reactants

Equation to calculate Gibbs free energy

ΔG = ΔH − TΔS

Unite for H?

Kj mol -1

What does it mean if Gibbs free energy is less than zero?

The reaction is feseable

Why do boh entalphy and entropy matter?

A negative H favours feseability

A positive S favours feseability

To calculate the temperature a reaction is feasible equation

T = ΔH / ΔS

Lattice entalphy are?

• always exothermic

• Magnitude indicates ionic bond strength

• Only for ionic compounds

• Can’t be measured directly

Is enthalpy of hydration endo or exothermic?

Exothermic

Is entalphy of hydration endo or exothermic

Both

Is the lattice enthalpy endo or exothermic

Exothermic

Entropy change with temperature

What does the sign with entropy mean?

Entropy positive= more disordered

Entropy negative= more ordered

What affects entropy?

State: solid liquid and gas

Amount of mol of gas

Haber process of solution for a negative solution

Haber process of solution for a positive solution

Haber process steps:

Formation → atomisation → ionisation → affinity → lattice enthalpy

Example of harber process