F335 - Oceans Flashcards
Change in entropy of the system =
Sum of change in enthalpy of products - Sum of change in entropy of reactants.
Entropy change if surroundings =
(- enthalpy change)/Temperature in kelvin
Change in total Entropy > 0
Reaction will occur spontaneously.
Change in total enthalpy = 0
Reaction is at equilibrium.
Lattice enthalpy of formation
The enthalpy change when one mole of a solid is formed from its separate gaseous ions. Always negative.
Ionic radius of an element depends on:
- The nuclear charge (atomic number) - the bigger the nuclear charge the smaller the item.
- The number of full energy levels-the more levels, the bigger the ion.
Enthalpy change of hydration.
The enthalpy change when an aqueous solution is formed from one mole of gaseous ion. Always negative.
Enthalpy change of solution.
The enthalpy change when one mole of solute dissolves to form a dilute solution.
Involves breaking down the lattice and then hydrating the gaseous ions produced (water is the solvent).
The acidity constant (Ka) is:
- Concentration of products/concentration of reactants.
- larger values mean stronger acids (an acid that will dissociated more).
- dependent on temperature
Calculating pH in strong acids:
Fully dissociate so [HA]=[H+]
pH = - log[H+ (aq)]
Calculating pH of weak acids:
[H+] = [A-]
Ka=[H+]^2/[HA]
pH = -log[H+]
How is Kw calculated (used for water)
Kw = [H+][OH-]
Definition of a buffer solution:
Solutions that will keep a constant pH despite dilution or addition of of small amounts of acid or alkali.
Why do buffer solutions remain a constant pH?
They contain large amounts of proton acceptors (a weak or conjugate base) and large amounts of proton donors (weak or to conjugate acids). Any additions of acid or alkali react with the large amounts and keep the pH constant within limits.
