Ch 17

• • First law of thermodynamics states that the energy of the universe is constant
  • Statement of law of conservation of energy 
  • Spontaneous process: Occurs without external intervention
  • Can be fast or slow 
  • A spontaneous process is one that occurs on its own, without any energy input from the outside. 
• • Domain of kinetics

  Rate of a reaction depends on the pathway from reactants to products

  = pathway of reactants and products

  • Thermodynamics 

  Provides information on whether a reaction is spontaneous based only on the properties of the reactants and products

  = only interested in final and initial state
• Entropy (S)

  • Thermodynamic function that describes the number of arrangements that are available to a system existing in a given state
  • Measure of molecular randomness or disorder
  • entropy, the measure of a system's thermal energy per unit temperature that is unavailable for doing useful work.
• Positional Probability 

  • Depends on the number of configurations in space that yield a particular state 
  • Gas expands into a vacuum to give a uniform distribution 
  • Expanded state has the highest positional probability of the states available to the system
• Positional Probability and Changes of State 

  • Positional entropy increases when going from solid to gaseous state 
• Entropy change when mixing two pure substances is expected to be positive 

  • Result of the presence of more microstates for the mixed condition 
  • Caused due to the increased volume available to a given particle after mixing occurs
  • Formation of solutions is favored by an increase in positional entropy that is associated with mixing
• Second Law of Thermodynamics

  • In any spontaneous process, there is always an increase in the entropy of the universe
  • First law of thermodynamics
  • Energy of the universe is constant
  • Energy is conserved, entropy is not 
• ΔSuniv Is positive 

  • Entropy of the universe increases
  • Process is spontaneous in the direction written 

  ΔSuniv is negative 

  • Process is spontaneous in the opposite direction

  ΔSuniv is zero

  • Process has no tendency to occur
  • System is at equilibrium 
• Standard State

  Standard state: Precisely defined reference state 

  A degree symbol on a thermodynamic function indicates that the corresponding process is carried out under standard conditions 
• • Positional probability determines the changes that occur in a chemical system 
  • Fewer the molecules, fewer the possible configurations 
• Third law of thermodynamics 

  • Entropy of a perfect crystal at 0 K is zero
  • Entropy of a substance increases with temperature
  • The third law of thermodynamics states that the entropy of a system approaches a constant value as the temperature approaches absolute zero.
• More negative the value ofΔG°, the further the reaction shifts to the right to attain equilibrium 
• System under constant P and T proceeds spontaneously in the direction that lowers its free energy 

  • Free energy of a reaction system changes as the reaction proceeds
  • Dependent on the pressure of a gas or on the concentration of species in solution
  • Equilibrium -Point where free energy value is at its lowest 
• For ideal gases:

  • Enthalpy is not pressure-dependent 
  • Entropy depends on pressure due to its dependence on volume 
• At a given temperature for 1 mole of ideal gas:

  • S large volume> S small volume

  Or,

  • S low pressure > S high pressure 
• G and K

  
• Maximum possible useful work obtainable from a process at constant temperature and pressure is equal to the change in free energy

  • Achieving the maximum work available from a spontaneous process can occur only via a hypothetical pathway
  • Any real pathway wastes energy
• Reversible process: Universe is exactly the same as it was before a cyclic process

  Irreversible process: Universe is different after a cyclic process 

  • All real processes are irreversible
  • Characteristics of a real cyclic process
  • Work is changed to heat 
  • Entropy of the universe increases 
• enthalpy changes alone are not enough to predict solubility—we must also consider entropic effects.

  
  

  KCl, LiF, CaS = S(system/solution) = negative