"Published in Newark, California, USA"
The following reaction
was allowed to proceed to equilibrium. The contents of the two-liter reaction vessel were then subjected to analysis and found to contain 1.0 mole H2S, 0.20 mole H2, and 0.80 mole S2. What is the equilibrium constant Keq for this reaction?
Solution:
Since the amount of H2S, H2, and S2 are given already in moles and they are in a 2L reaction vessel, then we can calculate their concentration in molarity.
Molarity of H2S:
Molarity of H2:
Molarity of S2:
Consider the given reaction
The equilibrium constant for the reaction is
The coefficient of each substance in the reaction is equal to the exponent of each factor for the equation above. The units of concentration of substances are always in molarity. Therefore, the equilibrium constant for the reaction is
Note: Usually, the value of Keq is unitless because the units of the concentration of substances are not included in the substitution to the equation of chemical equilibrium. If Keq = 0, then no reaction nor conversion of reactants to products involved in the process and on the other hand, if Keq = ∞, then the reaction is 100% complete in the process.