GenChem Week 1

• Spontaneous


  It is a reaction that does occur under the given set of conditions
• Nonspontaneous Reaction


  It is the reaction does not occur under specified conditions
• The reason being in is the Second law of thermodynamics- states that the state of entropy of the entire universe, as an isolated system, will always increase over time. The changes in the entropy in the universe can never be negative
• Entropy


  • A thermodynamic quantity
  • It is used to measure how spread out or dispersed the energy of a system is
  • It is used to described if the process is spontaneous and can occur in a defined direction or non-spontaneous and will occur in the reverse direction
  • It is considered as a state function
  • It is also a measure of how random or disorder the system is
• Factors that affect entropy


  • Number of Possible Microstate
  • Phases
  • Temperature
  • Mixture vs. Pure Solvent
  • Dissolved Substances vs. Precipitate
  • Presence of Gas
• The greater the number of possible microstate for a system the higher Entropy
• Gases have higher entropy than liquids, and liquids have higher entropy than solids
• The higher the temperature, the higher the entropy. Because of the corresponds kinetic Energy
• Compared to a pure substance, in which all particles are identidical, the entropy of a mixture of 2 or more different particle types is greater
• The side of the equation with more molecules of gas has higher Entropy. This is because a greater number of moles indicates a greater number of gas particles and greater arrangements of gas particles
• Melting


  1. Increase in entropy

  2. Spontaneous
• Vaporization


  1. Increase in entropy

  2. Spontaneous
• Dissolving


  1. Increase in entropy

  2. Spontaneous
• Heating


  1. Increase in entropy

  2. Spontaneous
• Gibbs Free Energy


  Used to predict whether the reaction or process will be spontaneous or non-spontaneous
• Conditions for Gibbs Free Energy

  • ΔG < 0 - Reaction is spontaneous in the forward Direction
  • ΔG > 0 - Reaction is nonspontaneous. The reaction is spontaneous in the opposite direction.
  • ΔG = 0 - The system is at equilibrium. There is no net change.
• Factors affecting the sign of ΔG

  • ΔH negative, TΔS positive - Reaction spontaneous at all T
  • ΔH positive, TΔS negative - Reverse reaction is always spontaneous
  • ΔH positive, TΔS positive - Spontaneous at high T
  • ΔH negative, TΔS negative - Spontaneous at low T
• Calculating ΔH° and ΔS° for a reaction at 25°C


  1. Convert temperature to Kelvin

  2. Calculate ΔH°

  3. Calculate ΔS°

  4. Calculate ΔG
• The entropy is negative when the process is freezing, condensation, and deposition
• higher temperature means higher entropy
• low temperature means low entropy
• mixtures has higher entropy compared to pure solvent
• dissolved substances has higher entropy compared to precipitated
• entropy means disorder of the arrangements of phases
• Gibbs Free Energy predicts whether the reaction will be spontaneous or nonspontaneous
• when enthalpy is negative and the temperature and entropy is positive, G is negative
• when H is positive and T and S are negative, G is positive
• when H, T, and S are all positive, G is positive and is nonspontaneous
• when H, T, and S are all positive, G is negative and is spontaneous at high temperature
• when H, T, and S are all negative, G is negative and is spontaneous at low temperature
• when H, T, and S are all negative, G is positive and is nonspontaneous at high temperature
• entropy is positive if the processes involves melting, evaporation, and sublimation
• G is spontaneous if the sign is negative
• G is nonspontaneous if the sign is positive
• Josiah Williard Gibbs, the person behind the Gibbs Free Energy