Le Chatelier's Principle

1) At what times is the reaction at equilibrium?

• 10 min
• 20 min
• 30 min
• 40 min

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TRA-8.A

Recall that at t = 30 minutes additional NO2 is injected into the reaction vessel.

In the few minutes after this injection, what happens to the concentration of NO₂?

• increases
• decreases
• stays the same

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TRA-8.A

In the few minutes after this injection, what happens to the concentration of N₂O₄?

• increases
• decreases
• stays the same

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TRA-8.A

4) Upon addition of more reactants, what direction did the reaction proceed?

• left (reactants)
• right (products)
• neither direction was favored

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TRA-8.A

Now let’s examine the same question quantitatively. In Model I, just before the 30 minute mark the system is at equilibrium with [NO₂] = 0.20 M and [N₂O₄] = 0.80 M. Additional NO₂ is injected which raises the NO₂ concentration to 0.50 M.

(a) Write the Q expression for this reaction on your white board and show Mrs. Zaepfel

(b) Calculate Q immediately after the injection.

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TRA-8.A

Comparing the value of Q and K, determine the direction the reaction will proceed.

• left (reactants) because K < Q
• right (products) because K > Q
• neither direction as Q = K

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TRA-8.A

We can do the same analysis for a different situation. Imagine that at t = 30 we had injected enough N₂O₄ to 1.5 M, while leaving the concentration of NO₂ at 0.20 M.

Calculate Q and predict the direction the reaction will then proceed.

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TRA-8.A

When reactants are added, what direction does the reaction proceed?

• toward the reactants
• toward the products
• neither

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TRA-8.A

When products are added, what direction does the reaction proceed?

• toward the reactants
• toward the products
• neither

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TRA-8.A

According to LeChatelier’s Principle, what direction will a reaction proceed if reactants are added?

• toward the reactants
• toward the products
• neither

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TRA-8.A