Dynamic Equilibrium

• Dynamic Equilibrium: a state of balance between two (opposite) processes occurring at the same time.

  • Rate of forward rxn = Rate of reverse rxn
• Two types of Dynamic Equilibrium

  1. physical equilibrium
  2. chemical equilibrium
• Two conditions for a system to reach dynamic equilibrium:

  1. CLOSED SYSTEM: No reactant, product or energy can be added or can leave the system.
  2. REVERSIBLE PROCESS (indicated by ⇆)
• Physical Equilibrium: Phase Equilibrium

  • In a closed system, two phases can exist at the same time (coexist)
  • Balance of two different phases of matter
• Equilibrium exists between ice melting and liquid freezing

  • Rates of melting = Rate of freezing
  • Amounts of ice and water remain constant
  • H2O(s) ⇆ H2O(l)
• Physical equilibrium: Solution equilibrium

  • Solids and liquids: In a saturated solution, the rate of dissolving equals the rate of precipitation.
  • Saturated solution with extra undissolved solute
  • Gases and liquids: In a closed system saturated solution, the rate of dissolving equals the rate of vaporization
• Chemical Equilibrium: a reversible reaction in a closed system where:⇆

  1. Reaction must be reversible ⇆
  2. The rate of the forward reaction and the reverse reaction is the same
  3. The concentrations of the reactants and products are constant.
  4. Not equal; just stays the same

  Sample Reaction: N2 + 3H2 ⇆ 2NH3
• When we mix any concentrations of these gases at room temperature:

  1. Reaction starts, reactants are used up and products are produced
  2. After a certain amount of time, the concentration of the reactants and products become constant. (Chemical Equilibrium)