Understanding Equilibrium Constants With No Denominator

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SUMMARY

The discussion centers on the concept of equilibrium constants, specifically in the context of the reaction involving solid calcium sulfate (CaSO4) dissociating into aqueous calcium ions (Ca) and sulfate ions (SO4). The equilibrium constant (K) is defined as the product of the concentrations of the products, [Ca][SO4], without a denominator, which can be confusing. The clarification provided indicates that the concentration of solid CaSO4 remains constant and is often omitted in solubility product calculations, leading to the interpretation that K represents the maximum molarity achievable in solution.

PREREQUISITES
  • Understanding of chemical equilibrium principles
  • Familiarity with solubility product constants (Ksp)
  • Knowledge of aqueous and solid phase distinctions in chemical reactions
  • Basic grasp of molarity and concentration calculations
NEXT STEPS
  • Study the concept of solubility product constants (Ksp) in detail
  • Learn about the role of solid reactants in equilibrium expressions
  • Explore the implications of equilibrium constants on reaction dynamics
  • Investigate the calculation of molarity in saturated solutions
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Chemistry students, educators, and professionals involved in chemical research or education, particularly those focusing on equilibrium and solubility concepts.

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Lets say you have something like
CaSO4 (s) <-----> Ca (aq) + SO4(aq)

The equilibrium constant would then have no denominator. That makes no sense to me!

K would equal [ Ca ][ SO4 ].

Wouldn't that then represent a constant amount of moles no matter how much CaSO4 is present?

Lets say K = 4 in this case
and [ Ca ] = 2 and [ SO4 ] = 2

Because K isn't a fraction, there is no way to reach equilibrium by balancing the reactant and products. K would then suggest the maximum molarity for a given solution, no matter how much solid reactant is in the solution.

That's how I'm interpreting it but it just seems wrong. Can someone clarify for me?

Thanks
 
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The concentration of CaSO4 in solid CaSO4 is a constant. Multiplying the inverse of that constant by [ Ca ][ SO4 ] gives you your K. Sometimes the constant is not shown (like in solubility products).
 
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