Equilibrium constant

How can we put a number to the state of equilibrium? This episode introduces the **Equilibrium Constant (K)**, a single value that quantifies the relationship between products and reactants in a reaction at equilibrium. Building on our understanding of what equilibrium is, we will learn how to write the equilibrium expression for any reversible reaction. Most importantly, you will discover how to interpret the magnitude of K to predict whether a reaction favors the products, favors the reactants, or exists as a balanced mixture, providing a powerful tool for understanding chemical systems.

Check your understanding

These are the same multiple-choice questions you will see in the Quiz section after you listen to the episode. Use them here to preview or review the answers.

What is the primary information provided by the equilibrium constant (K)?

  1. The time it takes for a reaction to reach equilibrium.
  2. The ratio of product concentrations to reactant concentrations at equilibrium.
  3. The change in temperature during a reaction.
  4. The activation energy of the forward reaction.
  5. The physical state of the products.

A chemical reaction has an equilibrium constant, Kc, with a very large value (K >> 1). What does this imply about the reaction at equilibrium?

  1. The reaction is very slow.
  2. The equilibrium mixture consists almost entirely of reactants.
  3. The equilibrium lies to the right, favoring the formation of products.
  4. The concentrations of reactants and products are nearly equal.
  5. The reaction goes essentially to completion.

For the reversible reaction used to make methanol, CO(g) + 2 H₂(g) ⇌ CH₃OH(g), what is the correct equilibrium constant expression (Kc)?

  1. [CH₃OH] / ([CO][H₂])
  2. [CO][H₂]² / [CH₃OH]
  3. [CH₃OH] / ([CO][H₂]²)
  4. [CO] + 2[H₂] / [CH₃OH]
  5. [CH₃OH] / (2[CO][H₂])

When writing an equilibrium constant expression for a heterogeneous reaction, which types of substances are generally excluded?

  1. Gaseous reactants
  2. Aqueous ions
  3. Pure solids
  4. Pure liquids
  5. Catalysts

Which of the following statements about the equilibrium constant, K, are true?

  1. Adding a catalyst increases the value of K.
  2. For a given reaction, the value of K is constant at a fixed temperature.
  3. A very small K value (K << 1) indicates that the equilibrium favors the reactants.
  4. The value of K depends on the initial starting concentrations of the reactants.
  5. K is a unitless quantity.

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