thermodynamics

• Spontaneous Process


  A process that does not need the application of energy to take place
• Spontaneous Process


  • Magnesium ribbon and hydrochloric acid (magnesium metal instantly disappears with the evolution of heat and gas is irreversible)
• Nonspontaneous Process


  A process that cannot proceed unless there is a driving force or outside help that acts on the system
• Nonspontaneous Process


  • A ball cannot be brought uphill unless someone pushes it
• Entropy (S)


  A measure of randomness or disorder, the amount of unusable energy of a system for every process as it approaches its end state
• Increase in entropy is the driving force for a spontaneous process
• Change in entropy (∆S)

  Depends only on the entropies of the final and initial states of the system, calculated as ∆S = Sfinal - Sinitial
• Positive value of ∆S (∆S>0)


  Indicates that the final state is more random or disordered than the initial state
• Negative value of ∆S (∆S<0)


  Indicates that the final state is more ordered than the initial state
• Factors that influence the amount of entropy

  • Change in Phase
  • Change in Temperature
  • Number of particles
• Change in Phase

  • Solid particles are confined to fixed positions, so entropy is relatively low
  • Liquid particles are slightly far apart, allowing limited movement, resulting in higher entropy than solids
  • Gas particles are very far apart, with great freedom of movement and kinetic energy, giving rise to greater entropy than liquids
  • Conversion of gas to liquid, and from liquid to solid, results in a decrease in entropy
• Change in Temperature

  • Rising the temperature increases the average kinetic energy of molecules, increasing entropy
  • Increasing temperature causes solid particles to vibrate more energetically, and liquid and gas particles to move about more rapidly, increasing entropy
  • Decreasing temperature results in lowering of entropy
• Number of Particles

  • More particles means more movement, noise, and disorder, increasing entropy
  • An increase in the number of particles, such as in the reaction A2B → 2A + B, increases the entropy
• Gibbs Free Energy (G)


  A measure of the maximum amount of work done in a thermodynamic system when the temperature and pressure are kept constant, usually expressed in Joules or Kilojoules
• Gibbs Free Energy (G)

  Equal to the enthalpy of the system minus the product of the temperature and entropy, G = H - TS
• Gibbs Free Energy in Nonspontaneous Processes


  A measure of the minimum amount of work that must be done on the system in order to drive the reaction
• ΔG < 0

  Reaction is spontaneous in the forward direction
• ΔG > 0

  Reaction is nonspontaneous in the forward direction, work must be supplied to make it occur
• Second Law of Thermodynamics

  • For natural processes, the change in entropy will be greater than zero
  • Natural systems tend to go towards disorder
  • For natural spontaneous processes, the entropy of the system tends to increase
• Thermodynamic systems can be classified as open (exchange matter with surroundings), closed (no exchange of matter but heat transfer is possible), or isolated (neither matter nor energy exchanged).
• The second law of thermodynamics states that the total entropy of an isolated system can never decrease over time, and is constant in a reversible process.
• The second law states that the total entropy (disorder) of an isolated system always increases over time.
• Entropy is a measure of disorder or randomness in a system.
• Increasing temperature increases entropy due to increased molecular motion.
• Adding more particles to a system also increases entropy.
• Entropy is a measure of the amount of randomness or disorder in a system.
• Chemical Equilibrium


  Also called dynamic equilibrium. A state in which the rate of the forward reaction equals the rate of the backward reaction. No net change in concentration of reactants and products.
• What happens in a reversible reaction?


  In reversible reactions, the reactants are not completely converted into products and some of the products may be converted back into reactants.
• Irreversible reaction


  Indicated by a single-headed arrow (→) in the chemical equation
• Reversible reaction


  Indicated by a double-headed arrow (⇌) in the chemical equation, showing the forward and backward reactions occurring simultaneously
• Le Chatelier's Principle


  States that if a stress (changes in reaction conditions) is applied to a system in equilibrium, then the systems adjust in order to reduce the effect of the stress applied.