GenChem 2

• Chemical Thermodynamics

  deals with the energy and entropy changes, and spontaneity of a chemical process.
• Spontaneous Processes


  processes taking place on their own without any external aid.
• Spontaneous Process Examples

  • Hot iron cools
  • Ice cube melts
  • Sugar dissolves in water
  • Gas escapes and spreads into all available space.
• Nonspontaneous Processes

  Changes that do not happen on their own
• Nonspontaneous Processes Examples

  • unplugged iron getting hotter
  • water freezing into ice cube by itself
  • sugar and water separating
  • scattered gas molecules returning to the container
• Spontaneous Reactions

  Endothermic (sometimes exothermic), even have ∆H = 0.
• Disordered or Random

  Final state of spontaneous processes
• Spontaneity

  Related to an increased in randomness
• Reason of increased Entropy

  When a pure liquid or solid dissolves in a solvent
• Factors

  • Temperature Changes
  • Physical State or Phase Changes
  • Dissolution of a solid or liquid
  • Dissolution of a gas
  • Atomic size or molecular complexity/ number of molecules
• Second Law of Thermodynamics

  all spontaneous processes are accompanied by increase in the entropy of the universe.
• System

  process/reaction whose thermodynamic change is being studie
• Surrounding


  the part of the universe that interacts with the system.
• Thermodynamic Free Energy

  • maximum amount of chemical energy derived from a spontaneous reaction that can be utilized to do work or to drive a nonspontaneous process.
  • minimum amount of energy that must be supplied to make a nonspontaneous reaction occur.
• First Law of Thermodynamics

  • Energy can be neither created nor destroyed
  • The energy of the universe is constant
• Potential Energy

  • broken in chemical bonds in compounds A and B
  • is the chemical bonds of C and D is lower
• Characteristics of Spontaneous Processes

  • may be fast or slow
  • occur without outside intervention
• Conversion of graphite to diamond

  Slow
• Kinetics

  Concerned with speed
• Thermodynamics

  Concerned with initial and final state
• Increase in the entropy of the universe 


  driving force for a spontaneous process
• Entropy (S)

  • thermodynamic function describing the number of arrangements that are available to a system
  • measure of the randomness or disorder
• Highest probabilities of existing stability

  Where nature proceeds
• Positional Entropy


  probability of occurrence of a particular state depends on the number of ways (microstates) in which that arrangement can be achieved
• Heat flow

  Determines the entropy changes in the surrounding
• Temperature

  Magnitude of the entropy depends on
• Lower Temperature

  Higher impact to the surroundings of the transfer of energy
• Enthalpy

  • concerns the system
  • measurement of energy in thermodynamic system
• Free Energy (G)

  • energy available to perform work
  • determines whether a process is spontaneous or not (DG = negative = spontaneous)
• Josiah Gibbs

  • Gibbs’ Free Energy
  • Physics professor at Yale during the late 1800’s who was important in developing much of modern thermodynamics
  • Takes into account enthalpy, entropy, and temperature symbol
• During a reaction

  • Reactant particles must physically collide
  • They must collide with enough energy to break the bonds in the reactant
• Change in Positional Entropy

  Dominated by the relative numbers of molecules of gaseous reactants and products
• More entropy

  More moles of Gas
• Third Law of Thermodynamics

  • The entropy of a perfect crystal at O K is zero
  • No disorder, since everything is in perfect position
• No movement

  0K
• No disorder

  No entropy
• Standard State

  One set of conditions at which quantities can be compared
• Standard Free Energy Change (DG0)

  • change in free energy that will occur if the reactants in their standard states are converted to the products in their standard states
  • cannot be measured directly
• Equilibrium

  Lowest possible free energy position for a reaction
• Rate of Chemical Reaction

  • speed by which reactants are converted to products.
  • Is measured by a change in the concentration of the reactants and products. As the reactants disappear, products appear.