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Chemical Thermodynamics: Entropy quiz

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  • What does the second law of thermodynamics state about entropy in the universe?
    The second law states that the entropy of the universe is always increasing, meaning the universe becomes more disordered over time.
  • How does entropy change during the phase transition from solid to liquid to gas?
    Entropy increases as you move from solid to liquid to gas because the molecular disorder and spacing increase.
  • What is the sign of delta S when a substance changes from solid to liquid or liquid to gas?
    The sign of delta S is positive, indicating an increase in entropy.
  • What happens to entropy when a substance changes from gas to liquid to solid?
    Entropy decreases, so the sign of delta S is negative.
  • What does the third law of thermodynamics state about entropy at absolute zero?
    The third law states that entropy reaches zero at absolute zero (0 Kelvin), where all molecular motion stops.
  • Why is absolute zero considered theoretical in thermodynamics?
    Absolute zero is theoretical because it has never been observed; the lowest natural temperature is about 2 Kelvin.
  • When comparing covalent compounds, what is the first factor to consider for entropy?
    The first factor is the phase of the compound; gases have the highest entropy, solids the lowest.
  • If covalent compounds are in the same phase, what is the next factor used to compare their entropies?
    The next factor is the number of microstates, which relates to the complexity and number of elements in the compound.
  • How does molecular mass affect entropy when comparing covalent compounds of equal phase and complexity?
    Greater molecular mass results in higher entropy.
  • What is lattice energy in the context of ionic compounds?
    Lattice energy is the energy released when one mole of an ionic compound forms from its gaseous ions.
  • How is lattice energy estimated for ionic compounds?
    Lattice energy is estimated by multiplying the absolute values of cation and anion charges and dividing by the sum of their radii (period numbers).
  • What does a higher lattice energy indicate about an ionic compound's properties?
    Higher lattice energy means stronger ionic bonds, higher boiling and melting points, and lower entropy.
  • What is the trend of lattice energy across the periodic table?
    Lattice energy increases as you move toward the top right corner of the periodic table.
  • Why do gases have higher entropy than solids?
    Gases have higher entropy because their molecules are more spread out and disordered compared to solids.
  • How does the number of elements in a covalent compound affect its entropy?
    More elements mean greater complexity, more microstates, and higher entropy.