Lechatelier's Principle Concentration Effects

Lechatelier's Principle Concentration Effects

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Multiple Choice

What is "equal" at equilibrium?

• The concentrations of reactants and products.

• The rate of the forward and reverse reactions.

• The sum of the coefficients of the reactants are equal to the sum of coefficients of the products.

Multiple Choice

When you disrupt or "stress" an equilibrium system by "adding" reactant, the system will attempt to do the "opposite" action in order to relieve the stress.

What action would be the opposite of "adding a reactant"?

• removing some of the reactant

• adding more reactant

Multiple Choice

The stress of "adding" more reactant disrupts the equilibrium system. In order to re-establish equilibrium, the system will favor the forward reaction to relieve the stress of adding a reactant.

Why must the forward reaction be favored to re-establish equilibrium, after adding a reactant?

• reactants must be removed to counter-act the addition of a reactant and reactants are consumed or "removed" in the forward direction.

• more reactant must be made to counteract the addition of a reactant and reactants are are produced or "made" in the reverse direction.

Explanation:

• Question: Why must the forward reaction favored to re-establish equilibrium?

• Answer: The stress is "adding" reactant. The system will attempt to counter-act the stress, by doing the OPPOSITE; since the opposite of "adding" is "removing", the system favors the forward reaction, because reactants are consumed or "removed" in the forward direction.

Multiple Choice

Consider the equilibrium system illustrated in the image.

Removing the product NH₃ is the "stressor".

To counter-act the stress, the system must do the opposite of "removing product".

How will our equilibrium system react to the stress of REMOVING the PRODUCT ammonia?

• the system will shift to the right to favor the formation of more product.

• the system will shift to left in order to favor the formation of more reactants.

• there will be no change in the equilibrium system.

Explanation:

• Removing product (the "stress") causes the system to do the opposite; make MORE product

• The system "shifts right", meaning the rate of the forward reaction speeds-up so more products are formed to partially undo the stress of removing a product.

Multiple Choice

Adding H₂, "stresses" or disturbs the equilibrium system.

The system will respond by favoring the reaction that will counter-act or partially undo the stress.

The opposite of adding the reactant is removing reactant.

Which reaction (forward or reverse) will be favored to remove some of the extra reactant that was added?

• The forward reaction is favored to remove reactant.

• the reverse reaction is favored to remove reactant.

Explanation:

• Adding reactant (the "stress") causes the system to do the opposite; REMOVE, use-up or "consume" some reactant.

• The system "shifts right", meaning the rate of the forward reaction speeds-up so more reactant is used-up or remove from the system to partially undo the stress of adding a reactant.

Multiple Choice

Consider the concentration profile (actually a partial pressure vs time curve) in the image provide with this question.

The profile shows that the system is initially at equilibrium, before the system is disturbed.

What feature of the concentration profile indicates that the system is initially at equilibrium?

• the partial pressure or amount of all reactants and products is NOT changing with time.

• the partial pressure or amounts of reactants and products are all equal.

Multiple Choice

Consider the image provided describing our equilibrium system: N₂ (g) + H₂ (g) ⇌ 2NH₃ (g)

After the addition of hydrogen, the system shifts to favor the forward reaction. How has the hydrogen concentration changed once equilibrium is established?

• Hydrogen concentration is LOWER because the reactions shifts right, consuming reactant to re-establish equilibrium.

• Hydrogen concentration is HIGHER, but less than the amount originally added because the equilibrium shifted right to partially undo the stress.

Explanation:

• The Hydrogen concentration is HIGHER, but less than the amount originally added because the equilibrium shifted right to partially undo the stress.

• It is important to understand that the "stressor" can not be completely undone, it can only be partially off-set.

Multiple Choice

Answer the question in the image (be careful, and review the explanation to the previous question if you are "stuck"

• option 1

• option 2

• option 3

• option 4

• option 5

Multiple Choice

Consider the equilibrium system:

CaCO₃ (s) ⇌ CaO (s) + CO₂ (g)

Which of the following options is the law of mass action for this process?

Multiple Choice

Answer the question in the image (careful!).

• option A

• option B

• option C

Explanation:

• You MUST write out the equilibrium constant expression for all equilibrium problems!

• If a substance does NOT appear in the equilibrium constant expression (e.g., pure solids and liquids) the system will not "shift" or be able to make any adjustments to small changes in the substance.

End Quizziz Lesson

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