Enthalpy, entropy and free energy

-the formation of one mole of an ionic lattice from it’s gaseous ions -used to measure strength of ionic bonds in a giant ionic lattice (more negative = stronger)

• the larger the ionic charge the stronger the lattice enthalpy because electrostatic attraction is greater • the smaller the radius of the charge the stronger the lattice enthalpy because charge density is higher and ions pack more closely together

the heat energy transferred in a reaction at constant pressure - kJ mol-1 - exothermic reactions have negative enthalpy values - endothermic reactions have positive enthalpy values

to measure lattice enthalpy of an ionic compound in an indirect pathway because it is impossible to do so directly

enthalpy change when one mole of a substance is formed from it’s constituent elements - usually exothermic

enthalpy change when each atom/ion in one mole of gaseous ions/atoms loses one electron to form one mole of gaseous positive ions - endothermic

enthalpy change when each atom/ion in one mole of gaseous atoms/ions gains one electron to form one mole of gaseous negative ions - exothermic for first electron affinity - endothermic for second electron affinity (repulsion) - -

enthalpy change when one mole of gaseous atoms is produced from an element in it’s standard state - endothermic

enthalpy change when one mole of gaseous ions becomes hydrated and aqueous (dissolved in water) - exothermic

enthalpy change when one mole of an ionic solid dissolves in excess water, becoming aqueous

Esol = Elatt + Ehyd

• if sum of hydration enthalpies is larger than sum of lattice enthalpies, overall enthalpy will be exothermic and compound will dissolve

a measurement of disorder in a system, which has a greater value when there’s more dispersion of particles

• physical state ( gas > liquid > solid ) • more particles = increased entropy

sum of entropy of products - sum of entropy of reactants

it depends on entropy change, enthalpy change and temperature of the system - when G is negative, reaction is feasible (spontaneous) - exothermic reactions are more likely feasible as enthalpy is negative, G is more likely to be less than 0 - endothermic reactions may be feasible at higher temperatures

G = H - TS - J mol-1

• if H is negative and S is positive, G is - and reaction will be feasible • if H is positive and S is negative, G is + and reaction isn’t feasible at any temperature • if both H and S are positive, reaction is only feasible above a specific temperature • if both H and S are negative, reaction is only feasible below a specific temperature

• indicates if a reaction is thermodynamically feasible, but doesn’t account for the reaction’s rate or kinetic • some reactions with a negative G may be happening so slowly that they are unobservable, due to high activation energy