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Equilibrium & Equilibrium Graphs

Chemistry: IB Diploma Higher Level, topic 5.5.1

Equilibrium & Equilibrium Graphs

Reversible reactions proceed in both forward and reverse directions. Equilibrium occurs when the rates of the forward and reverse reactions are equal. This can be demonstrated on concentration graphs.

Reversible reactions

Reversible reactions

  • Reversible reactions proceed in both forward and reverse directions.
  • When the rates of the forward and reverse reactions are equal, the concentrations of the reactant and product species remain constant over time.
  • At this point, the system is at equilibrium.
  • The relative concentrations of reactants and products in equilibrium systems vary greatly.
  • Some systems contain mostly products at equilibrium, some contain mostly reactants, and some contain appreciable amounts of both.
Concentration graphs example

Concentration graphs example

  • The decomposition of colorless dinitrogen tetroxide to yield brown nitrogen dioxide, an elementary reaction described by the equation:
  • N2O4(g)⇌2NO2(g)
  • A sealed tube containing colorless N2O4 darkens as it decomposes to yield brown NO2.
  • Changes in concentration over time as the decomposition reaction achieves equilibrium.
  • At equilibrium, the forward and reverse reaction rates are equal.
Concentration graphs

Concentration graphs

Test yourself on Equilibrium & Equilibrium Graphs

  • When does equilibrium occur?

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