5. A common way of treating wastewater contaminated with heavy metals is by use of precipitation. Many hazardous metals form highly insoluble precipitates with hydroxide, carbonate or sulphide. An industry produces a lead-containing wastewater, and wishes to remove the lead via precipitation with sulphide (S²-) ions, taking advantage of the following reaction: PbS(s) Pb²+ (aq) + S² (aq) Write an expression for the equilibrium constant for this reaction. The equilibrium constant for a precipitation reaction is known as the solubility product and is abbreviated by Kp.
Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Solubility product: It is the constant value written for the decomposition reaction of solids. For this reaction, the substance in the solid state is not included in the equilibrium constant expression.
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