Which phase change absorbs heat energy from the environment? A clear look at melting and evaporation.

If you’re brushing up for the SDSU placement assessment and irritation-free, this little thermodynamics detour is worth your time. Phase changes aren’t just party tricks for cold drinks and hot summers; they’re crisp demonstrations of heat moving in and out of matter. The question below pops up often enough to deserve a clear, human-friendly answer.

Which phase change absorbs heat energy from the environment?

A. Freezing

B. Melting

C. Evaporation

D. Condensation

Let me explain the quick science behind it, because the real story isn’t a one-liner.

Two big ideas you’ll use over and over

• Endothermic vs exothermic: An endothermic process grabs heat from the surroundings. An exothermic process gives heat to the surroundings. Think of endothermic as a heat sponge, and exothermic as a heat candle.

• Latent heat: When a substance changes phase, it often does so at a nearly constant temperature. The energy you add or remove goes into breaking or forming the bonds that hold particles in place, not into warming or cooling the whole substance right away. Those “hidden” energies have names—fusion/fusion heat and vaporization heat (or enthalpy of fusion and enthalpy of vaporization).

Now, back to the question. Among the options:

• Freezing (solid to liquid? No—freezing is actually liquid to solid) releases heat. It’s exothermic.

• Melting (solid to liquid) absorbs heat. It’s endothermic.

• Evaporation (liquid to gas) absorbs heat. Also endothermic.

• Condensation (gas to liquid) releases heat. It’s exothermic.

So, what absorbs heat? Melting and evaporation both do. If you’re answering strictly from the four choices, you’ve got two valid endothermic transitions in this set. That’s not a trick you want to miss on a real assessment, because it highlights an important nuance: endothermic does not mean “one answer only” in every multiple-choice moment. It means “this process requires heat input.” Two processes in the list meet that criterion.

Here are the clean takeaways you can carry into your study notes (and into the test room, if you ever end up there with a sheet of scratch paper in hand).

1. Melting = solid → liquid, energy in

• When a solid starts to melt, its particles need to break the organized lattice or rigid structure that keeps them stuck in place.

• The energy you supply goes into weakening those bonds, not into heating all the molecules up to a higher temperature (at the melting point, temperature can be constant while the phase change happens).

• The energy per mole that has to be supplied to cause melting is called the enthalpy of fusion (ΔHfus).

2. Evaporation = liquid → gas, energy in

• In evaporation, surface molecules with enough kinetic energy break free from the liquid and enter the gas phase.

• Like melting, this requires energy input—this time to overcome intermolecular forces strong enough to keep the liquid together.

• The energy per mole here is the enthalpy of vaporization (ΔHvap), which is typically larger than ΔHfus for a given substance, explaining why boiling and evaporation often feel like bigger energy deals than melting.

3. The other two are heat-releasing changes

• Freezing (liquid → solid) releases heat as the particles lock into a fixed, orderly arrangement.

• Condensation (gas → liquid) releases heat as fast-moving particles get slowed and join the liquid phase.

A little memory aid

Two endothermic steps to remember: melt and vaporize. They both borrow heat from their surroundings to move particles apart. The mental shorthand? “Melt and vaporize soak up heat.” It’s simple, but it sticks when you’re faced with a curveball in a test question.

Why this matters outside the test

• Real-world intuition: When ice sits in a drink, it warms the beverage gradually as it melts, absorbing heat from the liquid. If you leave a pot of water uncovered and simmer it, some of the water will evaporate, pulling energy from the remaining liquid and the pot—cooling the surface slightly, at least until the heat supply keeps it going.

• Calorimetry basics: In labs, scientists measure heat flow to determine phase transitions. Understanding which processes are endothermic vs exothermic is foundational for interpreting heat curves and phase diagrams.

• Everyday tech: Refrigeration and air conditioning rely on evaporation and condensation cycles. The same energy bookkeeping—the heat absorbed during evaporation and released during condensation—powers those systems.

Digressions that still circle back

• Temperature plateaus aren’t magical; they’re thermodynamics in action. If you’ve ever watched ice melt in a glass or observed water boiling on a stove, you’ve seen a phase change that’s temporarily not changing the temperature, even though heat is flowing. The energy is doing the work of changing the phase, not heating the whole substance.

• Some substances don’t behave exactly the same way as water. Metals, salts, or organic crystals can show different ΔHfus and ΔHvap values, and some have polymorphism (where the same material can exist in more than one solid form with different energies). For your SDSU chemistry placement assessment, the principle holds: identifying endothermic vs exothermic steps is the key, even if the numbers change a bit.

How to think about this on the SDSU placement assessment (without overthinking)

• Look for energy direction: If the process requires heat input, mark it endothermic. If it releases heat, mark it exothermic.

• Keep the two endothermic processes in mind: melting and evaporation. If a question asks about “absorbing heat,” you should consider these two as primary candidates.

• Don’t panic at the temperature station. During the phase change, the temperature can stay fixed even as energy pours in or flows out. That’s the hallmark of latent heat in action.

To wrap it up

The immediate answer to the question, as written, is that both melting and evaporation absorb heat energy from the environment. If you’re someone who likes a single-letter answer because of test format, the point to remember is: there are two endothermic transitions among the options. Freezing and condensation, in contrast, release heat.

If you want to keep this resonance going in your notes, try a quick two-column cheat sheet:

• Column A: Phase Change (Melting, Evaporation)

• Column B: Heat Direction (Endothermic, absorbs heat; ΔHpositive; energy input)

And a tiny reminder: the language scientists use—endothermic and exothermic—highlights the energy flow more than the temperature outcome alone. The same energy move underpins your ice cube, your kettle, and your car’s cooling system.

One last thought: chemistry is full of this kind of elegant balance. Tiny particles, big ideas, and the same energy rules that show up in lab benches, classrooms, and real life. As you navigate the SDSU placement assessment or any other chemistry topic, grounding your understanding in these simple energy movements will keep you sturdy when the questions get trickier.

If you’ve got a specific scenario you’re curious about—like how a particular substance shifts between phases under different pressures, or how humidity might alter the rate of evaporation on a hot day—tell me. I’m happy to walk through the energy accounting step by step and connect it back to the core ideas you’ll rely on in your coursework and tests.