CHEMISTRY

• Entropy


  Measure of molecular randomness
• Solid


  • Has low entropy due to rigid structure
• Gases


  • Have very high entropy due to constant, random motion of molecules
• Entropy


  Measure of a system's thermal energy that is unable to do useful work
• State function

  -only the initial and final state of the system matter, not the process
• Temperature

  • Indefinitely lowering temperature will eventually result in condition with zero entropy (3rd law of thermodynamics)
• Number of Particles


  • Reactions that produce much higher number of product particles than reactants are spontaneous, which lead to increase in entropy (2nd law of thermodynamics)
• Particles in liquid state


  • More random than when in solid state because they can have vibrational, translational, and rotational motions while solid only vibrates
• Standard Molar Entropy

  
  

  is the entropy of 1 mol of a substance under standard condition (1 atm and 25°C)
• Gibbs' free energy


  Determines the direction of a reaction
• Spontaneity of a process

  • Depends on two thermodynamic quantities: Enthalpy and Entropy
• Enthalpy


  The heat released or absorbed by the reaction
• Entropy


  Measure of randomness of the molecules
• Gibbs free energy

  Combines enthalpy and entropy to ultimately determine the spontaneity of a reaction
• G < 0 (-)

  The reaction is spontaneous
• G > 0 (+)

  The reaction is nonspontaneous
• Standard free energy change


  Calculated using standard conditions: 1 atm and 25C
• Chemical equilibrium


  Reaction rates of the forward and the reverse reaction are equal
• Reversible reaction


  A reaction that can proceed in both forward and backward directions
• Chemical equilibrium


  Point at which both the forward and the reverse processes are taking place at the same rate
• Dynamic equilibrium


  Reaction is still ongoing even if the products' and reactants' concentration are constant
• Equilibrium constant (Kc)


  Measure of the molar concentrations of all the species in the reaction at equilibrium
• Kc > 1000 - higher concentration of products
• Kc < 0.001 - higher concentration of reactants
• 0.001 < Kc < 1000 - significant concentration on both sides
• When a reaction is at equilibrium

  1. Forward and reverse reaction happen at the same rate

  2. The forward and reverse constants (Kf and Kb) are also equal

  3. The concentrations of the reactions are constant