When the rate of evaporation equals the rate of condensation
Explanation:
In a dynamic equilibrium the rate of the forward reaction is equal to the rate of the backward reaction. In evaporation liquid is converted to gas phase and in condensation the gas or vapor is converted to the liquid phase. So dynamic equilibrium is reached when the rate of evaporation equals the rate of condensation.
If we ignore temperature equilibrium (since no data given), then dynamic equilibrium when the rate of evaporation equals the rate of condensation over a finite period of time and under constant temperature.
This is because at *dynamic* equilibrium, evaporation and condensation are both taking place continuously. If the rates are equal, then the mass of vapour and mass of liquid phases do not change, hence equilibrium. Dynamic because changes are still taking place.
Answer is: the ratio of amount NaOH reacting per unit amount FeCl₃ is 3 mol NaOH /1 mol FeCl₃.
Balanced chemical reaction: 3NaOH(aq) + FeCl₃(aq) → 3NaCl(aq) + Fe(OH)₃(s). NaOH is sodium hydroxide. FeCl₃ is iron(III) chloride. Coefficient for sodium hydroxide is three and for iron(III hydroxide is one.
