3.19C: Know that a Reversible Reaction can Reach Dynamic Equilibrium in a Sealed Container

REVERSIBLE REACTIONS: Reaction that can occur in both directions (reactants can react to form products, and products can react to form initial reactants)

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DYNAMIC EQUILIBRIUM: Condition that exists when rate of forward and backward reaction in a reversible reaction mixture is equal

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Example: The Reaction Between Hydrogen Gas and Nitrogen Gas to Make Ammonia:

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• When Nitrogen and Hydrogen are the only reactants present in reaction, rate of forward reaction is highest as concentrations of both Hydrogen and Nitrogen will be at their highest
• As the reaction continues, concentrations of Hydrogen and Nitrogen will gradually decrease to form product (Ammonia), therefore the rate of forward reaction will decrease

• As Hydrogen and Nitrogen will react to increase the concentration of Ammonia (product), the rate of backward reaction will therefore increase (Ammonia can decompose to reform Hydrogen and Nitrogen)
• However, as Ammonia can decompose to reform Hydrogen and Nitrogen (reactants), this reversible reaction can therefore reach dynamic equilibrium

Assuming that the reactions occur in a sealed container where the two reactions are interlinked and none of the Gas can escape, the rate of of forward reaction and backward reaction will eventually become equal:

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3H2 (g)      +      N2 (g)      ⇌      2NH3 (g)