AP Chemistry

Unit 7.2

DIRECTION OF REVERSIBLE REACTIONS

Unit 7.2

Enduring Understanding:

• Some reactions can occur in both forward and reverse directions, sometimes proceeding in each direction simultaneously

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Learning Objective:

• Explain the relationship between the direction in which a reversible reaction proceeds and the relative rates of the forward and reverse reactions

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Direction of Reversible Reactions

• In a reversible reaction at equilibrium the rate of the forward reaction is equal to the rate of the reverse reaction
• When the rate of the forward reaction (left to right, → ) is greater than the reverse reaction (right to left, ←) the reaction is NOT at equilibrium
• Forward reaction is favored
• The products are being made faster than the reactants
• There is a net gain in the amount of products
• The net gain of products will continue until equilibrium is reached

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Reactants

Products

Direction of Reversible Reactions

• When the rate of the reverse reaction (right to left, ←) is greater than the forward reaction (left to right, → ) the reaction is NOT at equilibrium
• Reverse reaction is favored
• The reactants are being made faster than the products
• There is a net gain in the amount of reactants
• The net gain of reactants will continue until equilibrium is reached

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Reactants

Products

Practice: I Do

1. The reaction N₂ + 3H₂ ⇌ 2NH₃ is at equilibrium at 500 K. What happens to the rates of the forward reaction if some NH₃ is added at time, t?

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Practice: I Do

• The reaction N₂ + 3H₂ ⇌ 2NH₃ is at equilibrium at 500 K. What happens to the rates of the forward reaction if some NH₃ is added at time, t?

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The rate of the reverse reaction will increase to reestablish equilibrium. The rate of the reverse reaction will be greater than the rate of the forward reaction, until equilibrium is reestablished.