Phase changes from solid to liquid and liquid to gas are...

Phase changes from solid to liquid and liquid to gas are...

• A. Exothermic
• B. Endothermic
• C. Isothermal
• D. Adiabatic

Answer: (B)

Endothermic. Phase changes from solid to liquid (melting) and from liquid to gas (vaporization) require energy to be absorbed from the surroundings. That energy goes into overcoming intermolecular forces and increasing the potential energy of the particles, not into raising their kinetic energy, so the temperature stays constant at the melting or boiling point while the transition occurs. The other terms describe heat being released (exothermic) or no temperature change or no heat exchange (isothermal or adiabatic), which don’t match what happens during these phase changes.

Endothermic. Phase changes from solid to liquid (melting) and from liquid to gas (vaporization) require energy to be absorbed from the surroundings. That energy goes into overcoming intermolecular forces and increasing the potential energy of the particles, not into raising their kinetic energy, so the temperature stays constant at the melting or boiling point while the transition occurs. The other terms describe heat being released (exothermic) or no temperature change or no heat exchange (isothermal or adiabatic), which don’t match what happens during these phase changes.