15.2 Entropy and Spontaneity

• First law of thermodynamics: Energy can be transferred from one form to another, but it cannot be created or destroyed.

  Second law of themodynamics: The greater the shift from energy being localized to being widespread amongst the particles, the lower the change of the particles returning to their original state and the higher the entropy of the system
• Entropy (S): is the measure of the distributiom of total available energy between the particles
• A reaction is spontaneous when it moves towards either completion or equilibrium under a given set of conditions without exernal intervention

  A reactions is non-spontaneous when they doe not take place under a given set of conditions
• Spontaneous reactions lead to a increase in the total entropy of the systen and surroundings

  Non-spontaneous reactions lead to a decrease in the total entropy of the system and Surroundings
• Calculating entropy changes

  ∆Stotal = ∑S(products) - ∑S(reactants)

  • The entropy are specific for different states of matter
  • The coefficients used to balance the euation must be applied to olar entropy values when calculating the overall entropy change
• Predictions of the direction of the reaction

  A) Spontaneous

  B) Equilibrium

  C) Non-spontaneous

  
• Gibbs free energy ( ∆G): the measure of the energy which is free to do useful work rather than just leave the system as heat
• G = H - TS
• ∆G = ∆H - T∆S
• Factors affecting ∆G and spontenaity of a reaction

  A) endothermic

  B) endothermic

  C) exothermic

  D) exothermic

  E) more disorder

  F) more order

  G) more disorder

  H) more order

  I) negative at high T

  J) always negative

  K) negative at low T

  L) spontaneous at high T

  M) Never spontaneous

  N) always spontaneous

  O) spontaneous at low T

  P) always positive

  
• Gibbs free energy change of formation: the free energy change when one mole of a coumpound is formed from its elements under standard conditions

  ∆Gf = ∑∆Gf(products) - ∑∆Gf(reactants)