Consider an equilibrium reaction aA+ bB ⇀↽ cC+ dD We do not specify any phases, as we will treat the reaction generally using activities. An equilibrium reaction is one that can proceed in both directions, as indicated by the ⇀↽ symbol replacing the usual −→ in the chemical equation. Recall that the molar free energy ∆Ḡj for compound j in the reaction in terms of its activity aj as ∆Ḡ = ∆Ḡ◦ +RT...

Spherical pellets of antimony sulphide were dissolved in 1 molar sodium hydroxide solutions at different temperatures. It was found that the shrinking core with ash layer model could satisfactorily explain the dissolution process. Using this model it was found that initially the rate controlling step is a chemical reaction with activation energy of 10.2 kJ/mol. As the ash layer builds up, diffu...