Which of the following changes of state releases thermal energy?

• A. Melting of ice to liquid water
• B. Evaporation of liquid ethanol to ethanol vapor
• C. Sublimation of dry ice (solid CO_2) to carbon dioxide gas
• D. Condensation of water vapor to liquid water

Answer: (D)

Verified step by step guidance

1. Understand that changes of state can either absorb or release thermal energy depending on whether the process requires breaking or forming intermolecular forces.
2. Recall that melting, evaporation, and sublimation are phase changes where a substance goes from a more ordered state to a less ordered state (solid to liquid, liquid to gas, solid to gas), which requires energy input and thus absorbs thermal energy (endothermic processes).
3. Recognize that condensation is the reverse of evaporation, where gas turns into liquid, and this process releases thermal energy (exothermic process) because intermolecular forces are being formed.
4. Apply this knowledge to the given options: melting ice, evaporating ethanol, and sublimating dry ice all absorb energy, while condensation of water vapor releases energy.
5. Conclude that the change of state that releases thermal energy is the condensation of water vapor to liquid water.