In the solubility context, what does Q stand for?

In the solubility context, what does Q stand for?

• A. Reaction quotient
• B. Equilibrium constant
• C. Solubility product
• D. Rate constant

Answer: (A)

Q in solubility contexts is the reaction quotient. It uses the actual concentrations of ions in solution for the dissolution reaction, so for a salt dissolving into A+ and B−, Q = [A+][B−]. This value is compared to Ksp, the solubility product constant, to determine what happens next: if Q < Ksp the solution is undersaturated and more solid can dissolve; if Q = Ksp the system is at equilibrium; if Q > Ksp the solution is supersaturated and precipitation occurs until Q returns to Ksp. This is different from the equilibrium constant K (which is a general symbol for equilibria) and from the rate constant, which relates to reaction speed.

Q in solubility contexts is the reaction quotient. It uses the actual concentrations of ions in solution for the dissolution reaction, so for a salt dissolving into A+ and B−, Q = [A+][B−]. This value is compared to Ksp, the solubility product constant, to determine what happens next: if Q < Ksp the solution is undersaturated and more solid can dissolve; if Q = Ksp the system is at equilibrium; if Q > Ksp the solution is supersaturated and precipitation occurs until Q returns to Ksp. This is different from the equilibrium constant K (which is a general symbol for equilibria) and from the rate constant, which relates to reaction speed.