During which phase change will 2 grams of water release 668 joules of heat energy?

• A. Evaporation of liquid water to vapor at 100^ext{o}C
• B. Freezing of liquid water to ice at 0^ext{o}C
• C. Condensation of water vapor to liquid at 100^ext{o}C
• D. Melting of ice to liquid water at 0^ext{o}C

Answer: (C)

Verified step by step guidance

1. Identify the phase changes involved and the associated enthalpy changes (heat absorbed or released) for water: evaporation, condensation, freezing, and melting.
2. Recall that evaporation and melting are endothermic processes (heat absorbed), while condensation and freezing are exothermic processes (heat released). Since the problem states heat is released, focus on condensation and freezing.
3. Find the molar mass of water to convert the given mass (2 grams) into moles: \(\text{moles} = \frac{\text{mass}}{\text{molar mass}} = \frac{2\,\text{g}}{18.015\,\text{g/mol}}\).
4. Use the known enthalpy values for the phase changes: enthalpy of vaporization \(\Delta H_{vap}\) (for evaporation/condensation) and enthalpy of fusion \(\Delta H_{fus}\) (for melting/freezing). Calculate the heat released or absorbed by multiplying moles by the appropriate enthalpy change: \(q = n \times \Delta H\).
5. Compare the calculated heat values for condensation and freezing to the given heat released (668 J) to determine which phase change corresponds to releasing 668 joules of heat.