Which state changes involve energy being absorbed?

Which state changes involve energy being absorbed?

• A. Freezing and condensation.
• B. Deposition and condensation.
• C. Boiling and freezing.
• D. Melting and sublimation.

Answer: (D)

Energy is absorbed whenever a substance moves to a higher-energy, less-ordered state. Melting, the change from solid to liquid, requires heat to break apart the rigid solid structure. Sublimation, solid to gas, needs even more energy to completely overcome intermolecular forces and disperse molecules into the gas phase. Both of these transitions are endothermic, so they involve taking in energy, which is why melting and sublimation is the correct pairing. In contrast, freezing and condensation release energy as the substance becomes more ordered (solid from liquid, liquid from gas). Deposition and condensation also release energy (gas to solid and gas to liquid). Boiling does absorb energy, but when paired with freezing, the set includes one that releases energy, so it’s not consistent with the idea of “energy being absorbed” for the whole change.

Energy is absorbed whenever a substance moves to a higher-energy, less-ordered state. Melting, the change from solid to liquid, requires heat to break apart the rigid solid structure. Sublimation, solid to gas, needs even more energy to completely overcome intermolecular forces and disperse molecules into the gas phase. Both of these transitions are endothermic, so they involve taking in energy, which is why melting and sublimation is the correct pairing.

In contrast, freezing and condensation release energy as the substance becomes more ordered (solid from liquid, liquid from gas). Deposition and condensation also release energy (gas to solid and gas to liquid). Boiling does absorb energy, but when paired with freezing, the set includes one that releases energy, so it’s not consistent with the idea of “energy being absorbed” for the whole change.