law 2 and 3

• Spontaneity of a process

  How it 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
• Almost all exothermic chemical processes

  Are spontaneous
• Spontaneous processes


  • Combustion reactions produce heat
  • Ice melts spontaneously into liquid water as it absorbs heat
  • Acetone and alcohols (volatile liquids) evaporate in a spontaneous endothermic process
• 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

  • Increase in randomness of a system
  • Decrease in randomness of a system
• Third law of Thermodynamics


  A perfectly ordered pure crystalline solid at zero Kelvin will have a zero entropy
• Raising the temperature of a system

  Increases the average kinetic energy and the freedom of motion of the particles in the system, thus increasing the entropy of the system
• Chemical reactions that produce higher number of product particles than that of reactant particles

  Are usually spontaneous
• Chemical reactions with fewer product particles than the reactants

  Are described to have negative entropy and are thus nonspontaneous
• Entropy as a function of temperature and phase change

  • In the solid phase range, the vibrational energy of the particles steadily increases
  • Once the melting point of the substance is reached, its entropy suddenly shoots up
  • Once the boiling point of the substance is reached, entropy abruptly increases
• Standard molar entropy


  The entropy of one mole of a substance at the standard conditions (1 atm and 25°C)
• Calculating the standard entropy of a reaction

  Obtained from the standard molar entropy values of the reactants and products
• The decomposition of CaCO3 gives a positive ΔS°, which means that the system is in a more random state under standard conditions than when CaCO3 is formed
• The Haber process for the industrial synthesis of ammonia is a process that involves gaseous species and is described to have achieved a state of less randomness
• Second law of Thermodynamics

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


  ΔStotal = ΔSsystem + ΔSsurroundings
• The positive ΔStotal signifies that the decomposition of H2O2 is spontaneous