THERMODYNAMICS

• Spontaneity


  How a process occurs on its own without the help of any external factors
• Spontaneity only tells whether a reaction will occur or not but will not predict the rate of a process
• Characteristics of spontaneous processes

  • Almost all exothermic chemical processes are spontaneous
  • Some spontaneous processes do not follow this generalization (e.g. ice melting, volatile liquids evaporating)
• Entropy


  A measure of molecular randomness

  
• Spontaneous processes occur from an ordered state to a more random arrangement
• Entropy is a state function, it only depends on the initial and final states of a system
• Factors that influence entropy

  • Raising temperature increases average kinetic energy and freedom of motion of particles, thus increasing entropy
  • Chemical reactions that produce higher number of product particles than reactants are usually spontaneous
  • Chemical reactions with fewer product particles than reactants have negative entropy and are nonspontaneous
• The Third Law of Thermodynamics states that a perfectly ordered pure crystalline solid at zero Kelvin will have zero entropy
• Entropy as a function of temperature and phase change

  1. In solid phase, vibrational energy of particles steadily increases

  2. At melting point, entropy suddenly shoots up due to rotational and translational movements

  3. Once all solid particles are liquefied, entropy returns to a steadily pattern

  4. At boiling point, entropy abruptly increases as gas particles are much freer to move

  
• Standard Molar Entropy


  Entropy value per mole of a substance
• Second Law of Thermodynamics


  For any spontaneous process, there is a net increase in the total entropy of the system and its surroundings
• Calculating entropy change in surroundings

  Entropy change in surroundings = -entropy change in system