Which of the following can we predict from an equilibrium constant for a reaction?
Which of the following can we predict from an equilibrium constant for a reaction?
1. the extent of a reaction
2. which direction a reaction will proceed by measuring the concentrations of reactants and products
3. whether a system is at equilibrium by measuring the concentrations of the reactants and products.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 2 only
E) 1, 2, and 3
Which of the following can we predict from an equilibrium constant for a reaction?
1. the extent of a reaction
2. which direction a reaction will proceed by measuring the concentrations of reactants and products
3. whether a system is at equilibrium by measuring the concentrations of the reactants and products.
A) 1 only
B) 2 only
C) 3 only
D) 1 and 2 only
E) 1, 2, and 3
1 Answer
Well, arguably, none of the above are actually useful aspects of a reaction that require an equilibrium constant to obtain...
But the intention of the question is probably that only
1. the extent of a reaction
This can be determined by using
#Q# OR#K# . The extent of reaction is simply given by#x# , i.e. the drop in concentration of the aqueous reactant(s) or the drop in partial pressure of the gaseous reactants.Since
#x# can be determined whether at equilibrium or not,#Q# can be used to find the extent of the reaction.However,
#K# is a measure of the maximum extent of the reaction.[It's not all that useful for that purpose because by definition, at equilibrium
#Q = K# , so you know the extent of reaction is#100%# at this point without ever using#K# directly.]
2. which direction a reaction will proceed by measuring the concentrations of reactants and products
This is the job of
#Q# , the not-yet-equilibrium constant.
- When
#bb(Q < K)# , the reaction is reactant-heavy and wishes to proceed forward, and vice versa.- When
#bb(Q = K)# , the reaction is at equilibrium, and thus the reaction has equal forward and reverse rates; it will not shift any more because the extent of reaction is#100%# (#Deltax = 0# ).
3. whether a system is at equilibrium by measuring the concentrations of the reactants and products.
Again, this is the job of
#Q# . This is mentioned in#(1)# and#(2)# in that at equilibrium,#Q = K# .If you choose to measure concentrations at some arbitrary time, then if
#Q# happens to be equal to#K# , the reaction is already at equilibrium.
