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Free Energy and Thermodynamics - General Chemistry

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  • What defines a spontaneous process?
    A spontaneous process occurs without ongoing outside intervention or energy input.
  • Is the conversion of diamond to graphite spontaneous?
    Yes, because graphite is more stable than diamond, the conversion is spontaneous but occurs at a very slow rate.
  • What is the sign of ΔH for an endothermic process?
    ΔH > 0 for an endothermic process, meaning heat is absorbed.
  • What is the sign of ΔH for an exothermic process?
    ΔH < 0 for an exothermic process, meaning heat is released.
  • How does entropy (S) relate to molecular disorder?
    Entropy is a thermodynamic function that increases with the number of energetically equivalent ways (microstates) to arrange a system, reflecting its degree of disorder or randomness.
  • State the Second Law of Thermodynamics in terms of entropy.
    For any spontaneous process, the entropy of the universe increases: ΔS_universe > 0.
  • How does entropy change with phase transitions?
    Entropy increases in the order: S(solid) < S(liquid) < S(gas).
  • What happens to entropy when volume increases?
    When volume increases, ΔS > 0 because energy is dispersed over a larger space.
  • What two thermodynamic factors affect reaction spontaneity?
    Change in enthalpy (ΔH) and change in entropy (ΔS) are the two main factors influencing spontaneity.
  • What is the relationship between ΔS_universe, ΔS_system, and ΔS_surroundings?
    ΔS_universe = ΔS_system + ΔS_surroundings, and for spontaneous processes, this sum is positive.
  • Why is melting of ice spontaneous at temperatures above 0°C despite being endothermic?
    Because the increase in entropy (ΔS) of the system favors spontaneity, overcoming the positive ΔH.
  • How is entropy change of surroundings related to enthalpy change of the system?
    At constant pressure and temperature, ΔS_surroundings = -ΔH_system / T.
  • What is Gibbs free energy (ΔG) and its relation to spontaneity?
    ΔG = ΔH - TΔS; a process is spontaneous if ΔG < 0, non-spontaneous if ΔG > 0, and at equilibrium if ΔG = 0.
  • How does temperature affect spontaneity when ΔH and ΔS have different signs?
    If ΔH > 0 and ΔS > 0, reaction is spontaneous at high temperatures. If ΔH < 0 and ΔS < 0, spontaneous at low temperatures.
  • What is the Third Law of Thermodynamics regarding entropy?
    The entropy of a perfect crystal at absolute zero (0 K) is zero: S = 0.
  • How does molar mass affect entropy?
    Larger molar mass generally leads to larger entropy due to more energy dispersal.
  • How does molecular complexity affect entropy?
    More complex molecules have higher entropy because they have more ways to distribute energy.
  • What is the formula to calculate standard entropy change (ΔS°) for a reaction?
    ΔS°_rxn = Σ n_p S°_products - Σ n_r S°_reactants.
  • How is standard Gibbs free energy change (ΔG°_rxn) calculated?
    ΔG°_rxn = Σ n_p ΔG°_f,products - Σ n_r ΔG°_f,reactants.
  • How is ΔG related to reaction quotient Q under nonstandard conditions?
    ΔG = ΔG° + RT ln Q, where R is gas constant and T is temperature.
  • What is the relationship between ΔG°, equilibrium constant K, and temperature?
    At equilibrium, ΔG = 0 and Q = K, so ΔG° = -RT ln K.
  • How can the temperature dependence of equilibrium constant K be expressed?
    ln K = (-ΔH°/R)(1/T) + (ΔS°/R), a linear relation useful to find ΔH° and ΔS°.