Entropy and the Spread of Energy · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

More Ways, More Entropy

Science · Chemistry · ages 17-18
Name ______________________   Date ____________

  1. What does a higher entropy mean for a system?

    • Its energy is hotter
    • Its energy and particles are more spread out
    • Its particles move more slowly

  2. Rank solid, liquid, and gas by entropy, highest first.

    • Solid, liquid, gas
    • Gas, liquid, solid
    • Liquid, gas, solid

  3. A reaction makes two moles of gas from solids only. What is the sign of the entropy change?

    • Positive, because gas appears where none stood
    • Negative, because solids vanish
    • Zero, because atoms are conserved

  4. Ammonium nitrate dissolves even though it cools the water. Why?

    • The ions spreading give an entropy gain that outweighs the enthalpy cost
    • Cooling always makes dissolving spontaneous
    • The water heats the salt from outside

  5. For X turning into Y + Z, standard entropies are X 100, Y 150, Z 120 in joules per mole per kelvin. Products sum minus reactants gives what value?

    Answer: ______________

  6. Entropy comes in joules per mole per kelvin and enthalpy in kilojoules. What must you do first?

    • Ignore the units and add directly
    • Divide the entropy value by 1000
    • Multiply the enthalpy value by 1000 twice

  7. A student says the ammonium nitrate solution cools, so its entropy must have fallen. This claim is true.

    Circle one:   True   False

  8. A solid carbonate decomposes into a solid oxide plus carbon dioxide. Predict the sign and reason.

    • Negative, because a solid breaks down
    • Zero, because moles of solid stay at one
    • Positive, because a gas appears where none stood
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Answer key

For grown-ups. Fold this page away before handing over the rest.

More Ways, More Entropy W1-mt_a_2feH2gnE-s1

  1. Its energy and particles are more spread out · Entropy counts arrangements, and more spread means more possible arrangements.
  2. Gas, liquid, solid · Particles gain freedom of movement at each stage, so gas tops the ranking.
  3. Positive, because gas appears where none stood · Turning solids into gas adds freedom, so entropy rises.
  4. The ions spreading give an entropy gain that outweighs the enthalpy cost · The endothermic cost is real, but the entropy gain from spreading ions is bigger.
  5. 170 · 150 + 120 - 100 gives an entropy change of 170 joules per mole per kelvin.
  6. Divide the entropy value by 1000 · Entropy must be in kilojoules before it can mix with enthalpy, so divide by 1000.
  7. False · Cooling shows endothermic enthalpy. Dissolving still raises entropy through spreading.
  8. Positive, because a gas appears where none stood · Making gas from solids adds arrangements, so the entropy change is positive.
Worksheet · LightMySky