Earth Science · Matter & Energy

When Gas Becomes Liquid: Condensation Up Close

Modeling the molecular moment water vapor turns back into liquid
SubjectScience
Grade7th Grade
Duration45 min
DateTue, Jan 20
TeacherMr. Hayes
01Learning Objectives
!

Pre-Lab Safety

Cold cups sweat — wipe spills immediately to prevent slips. The ice water is cold, not dangerous, but no ice down collars. Keep the cup on the tray, away from notebooks and electronics.

02Standards
MS-PS1-4 Develop a model that predicts changes in particle motion when thermal energy is added or removed.
MS-ESS2-4 Develop a model to describe the cycling of water through Earth's systems driven by energy.
SEP-2 Developing and using models to explain a phenomenon.
03Materials · per group of 3
1 metal cup + 1 room-temp plastic cup (the control)
Ice, water, and a thermometer
Dry paper towel + tray to catch condensation
Lab-notebook observation page + before/after model frame
Projected particle-motion animation (warm vs. cold)
Exit-ticket half-sheets
04Lesson Arc · 45 Minutes
Phenomenon Predict Investigate Model Exit
0:00–0:06
6 min
Phenomenon Hook
TeacherHold up a cold soda can that's been in the cooler. Ask: "Where did this water on the OUTSIDE come from? The can is sealed — so it can't be leaking." Take a few competing ideas, write them on the board, don't confirm.
StudentsJot a first explanation in the notebook, then share with an elbow partner. Notice the puzzle: water appears where there was none.
0:06–0:14
8 min
Make a Prediction
TeacherSet up the test: an ice-water metal cup and a room-temp cup side by side. Ask: "On which cup will water form, and why? Predict at the molecule level." Show the particle-motion animation: warm air = fast molecules.
StudentsWrite a prediction with a reason ("I think ___ because ___"), referencing whether molecules near the cup speed up or slow down.
Guiding question What happens to air molecules when they touch a very cold surface?
0:14–0:28
14 min
Investigate · Hands-On Test
TeacherDistribute trays. Circulate with probing questions: "Which cup is sweating? Touch the droplets — where is that water coming from, the inside or the air?" Have groups record the cup temperatures.
StudentsFill the metal cup with ice water, wait 3 minutes, and observe both cups. Record: which cup formed droplets, the temperature of each, and where on the cup the water collected.
0:28–0:38
10 min
Build the Molecular Model
TeacherLead the reveal: "Air holds invisible water VAPOR. The cold cup pulls energy out of nearby molecules — they slow down and clump into liquid: condensation." Model the before/after drawing on the board.
StudentsComplete the before/after model: fast, spread-out gas molecules → slow, close-packed liquid molecules, with an arrow labeled "loses energy / cools." Write one sentence tying it to the can.
0:38–0:45
7 min
Exit Ticket & Closure
TeacherConnect it back: "This is the same reason clouds and morning dew form." Distribute the exit ticket and remind students to use the word "energy" in their answer.
StudentsComplete the exit ticket independently, then revise their original board idea if the evidence changed their mind.
05The Model Students Build
Before · Water Vapor (gas)
Fast & far apart
High energy molecules bounce freely with lots of space between them.
After · Liquid Water
Slow & close-packed
Cooled molecules lose energy, slow down, and clump together as a droplet.
06Exit Ticket
Q1The cold cup got wet on the outside, but it was never opened. Explain where the water came from. Use the words "vapor," "energy," and "condensation."
Q2At the molecule level, what happens to air molecules when they touch the cold cup? (Circle one and explain: speed up / slow down.)
Q3Name one place outside this classroom where the SAME process happens.
What mastery looks like: The answer says vapor in the AIR (not water from inside) lost energy at the cold surface, slowed down, and condensed into liquid — and connects it to dew, clouds, or fog.
07Differentiation & Extensions

+Supports

  • Abstract particle idea: give a half-built model with the gas molecules already drawn, so students only add the cooled, clumped liquid state.
  • Multilingual learners: provide a word bank (vapor, condense, energy, molecule) with icons and a sentence frame for the exit ticket.
  • IEP-friendly move: assign the "recorder" role so the student documents observations while a partner handles the cold cup; accept a labeled diagram in place of a paragraph.

↗Extensions

  • Challenge: predict and test how breathing on a cold mirror compares to the cup — same process, different vapor source.
  • Connect to the full water cycle: where does evaporation supply the vapor that later condenses?
  • Quantify it: measure how the droplet amount changes if you start with warmer vs. ice-cold water, and graph the result.