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Difficulty: EasyThermodynamics and Heat

Arrange the following physical states and temperatures of water in order of increasing average molecular kinetic energy, from the lowest thermal energy state to the highest thermal energy state.

  1. 1Ice at −10∘C-10^\circ\text{C}
  2. 2Liquid water at 20∘C20^\circ\text{C}
  3. 3Liquid water at 100∘C100^\circ\text{C}
  4. 4Superheated steam at 120∘C120^\circ\text{C}

Answer

The correct sequence from lowest to highest molecular kinetic energy is: Ice at −10∘C-10^\circ\text{C}, followed by Liquid water at 20∘C20^\circ\text{C}, then Liquid water at 100∘C100^\circ\text{C}, and finally Superheated steam at 120∘C120^\circ\text{C}.
Temperature is directly proportional to the average kinetic energy of the molecules in a substance. In the solid phase (ice at −10∘C-10^\circ\text{C}), molecules vibrate minimally within a lattice. As thermal energy is added, ice melts into liquid water, where molecules move with greater kinetic energy at 20∘C20^\circ\text{C} and even faster at 100∘C100^\circ\text{C}. When vaporized into steam and heated to 120∘C120^\circ\text{C}, the gaseous molecules move freely at the highest average speeds, having the highest molecular kinetic energy.

Step-by-Step Solution

1
Relate temperature and phase state to molecular kinetic energy.
Temperature measures the average kinetic energy of constituent particles, while phase changes (solid to liquid to gas) require thermal energy input.
Particles in solids vibrate in place, liquids exhibit fluid molecular translation, and gases feature rapid, independent molecular motion.
2
Rank the solid and lower-temperature liquid states.
Ice at −10∘C-10^\circ\text{C} has less kinetic energy than liquid water at 20∘C20^\circ\text{C}.
Sub-zero solid ice possesses lower temperature and rigid intermolecular structure compared to liquid at room temperature.
3
Rank the higher-temperature liquid and gaseous states.
Liquid water at 100∘C100^\circ\text{C} is higher in kinetic energy than water at 20∘C20^\circ\text{C}, but lower than steam at 120∘C120^\circ\text{C}.
Molecules in gaseous steam at 120∘C120^\circ\text{C} move far more rapidly and independently than molecules in boiling liquid water.

Key Concept

Temperature as a measure of average molecular kinetic energy across solid, liquid, and gas phases
Estimated Time:45s
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Topics

Thermodynamics and Heat

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