AP Chemistry : System Equilibrium
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Example Questions
Example Question #1 : System Equilibrium
What is occuring when a mixture reaches a dynamic equilibrium state?
The forward and reverse reactions are occurring at the same rate
Only the reverse reaction is occurring
Only the forward reaction is occurring
Neither reaction is occurring; the mixture is completely static
The forward and reverse reactions are occurring at the same rate
Dynamic equilibrium means that the forward and reverse reactions are occurring at the same rate so that there is no net change in the concentrations.
Example Question #2 : System Equilibrium
Which of the following accurately describes what occurs in reversible reactions?
The reaction can proceed in the forward direction to completion.
The reaction can proceed in both the forward and reverse directions, and these reactions do not usually go to completion.
The reaction can proceed in both the forward and reverse directions, and these reactions always go to completion.
none of the above
The reaction can proceed in both the forward and reverse directions, and these reactions do not usually go to completion.
The definition of reversible reactions is that they are indeed reversible; in other words, they can proceed in the forward and reverse directions. Since the products can react as well to reform the reactants, these reactions usually do not proceed to completion and instead exist in a dynamic state.
Example Question #3 : System Equilibrium
Consider the following reaction:
The equilibrium constant, 
In a reaction flask, you have a solution containing ![[A]=0.332\hspace{1 mm}M](https://vt-vtwa-assets.varsitytutors.com/vt-vtwa/uploads/formula_image/image/21576/gif.latex)
![[B]=0.0200\hspace{1 mm}M](https://vt-vtwa-assets.varsitytutors.com/vt-vtwa/uploads/formula_image/image/21577/gif.latex)
![[C]=0.332\hspace{1 mm}M](https://vt-vtwa-assets.varsitytutors.com/vt-vtwa/uploads/formula_image/image/21578/gif.latex)
The reaction will proceed to the left
The reaction will not proceed
The reaction will proceed to the right
None of the available answers
The reaction will proceed both to the right and two the left, but at equal rates
The reaction will proceed to the left
For the reaction:
The expression for the equilibrium constant is:
![K_{eq}=\frac{[C]^2}{[A][B]^2}](https://vt-vtwa-assets.varsitytutors.com/vt-vtwa/uploads/formula_image/image/21580/gif.latex)
The reaction quotient is:
![Q=\frac{[C]^2}{[A][B]^2}=\frac{[0.332]^2}{[0.332][0.0200]^2}=830\hspace{1 mm}M^{-1}](https://vt-vtwa-assets.varsitytutors.com/vt-vtwa/uploads/formula_image/image/21581/gif.latex)
The reaction quotient is much larger than the equilibrium constant, so the reaction will proceed to the left.
Example Question #4 : System Equilibrium
Which of the following is not always true for the given arbitrary reaction in equilibrium?
The molar concentrations of reactants and products are equal
Each choice is always true for this equilibrium reaction
The forward and reverse reaction rates are equal
The molar concentrations of reactants and products are equal
The forward and reverse reaction rates are equal for reactions in equilibrium, however, the molar concentration of the reactants and products are usually not equal themselves. One can calculate the equilibrium constant using the equation below.
Example Question #86 : Reactions And Equilibrium
Determine the equilibrium expression for the following reaction:
Equilibrium expressions are a ratio of the concentration of products raised to the stoichiometric coefficient, divided by reactants raised to the stoichiometric coefficient. Solids are omitted from this expression.
For the generic example 
For our given reaction, we can find the equilibrium expression in a similar manner. Do not forget to omit the solid component of the reaction!
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