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Matter Lab 6-8 / Week 03 / Bench Day
6/6
Week 03 · Heat, Temperature and Changing State

Bench Day

Bench Day: Freeze and melt
// Faster particles, flowing heat and the points where matter changes
⏱ about 20 min

Bench Day: Freeze and Melt

Saturday morning, Rocket fills an ice tray at the sink and slides it into the freezer. "How long until it freezes?" he asks.

"Check every half hour," Raven says. "And we will time a melt at the same time." She sets an ice cube in a cup of warm tap water.

Nova hovers over the cup, where the cube is already shrinking. "What do you notice about the water and the cube together?" she asks.

"The cube is getting smaller and the water is getting colder," Rocket says, touching the cup.

"So heat is leaving the water and going into the ice," Raven says. "Warm to cold, like always."

An hour later, the tray in the freezer has a thin skin of ice on each cube. By lunch, they are solid.

Rocket writes both times in the Bench Log: freeze, and melt.

  1. Temperature measures the average kinetic energy of the particles in matter. Faster particles on average means hotter.
  2. Thermal energy is the motion of atoms and molecules inside a substance. Heat is that energy transferred from warmer to cooler until temperatures match.
  3. Celsius puts water freezing at 0 and boiling at 100. Fahrenheit uses 32 and 212. Kelvin starts at absolute zero, 273.15 below freezing.
  4. The melting point is where a solid becomes a liquid, and it equals the freezing point. The boiling point drops at high altitude.
  5. Evaporation turns liquid to gas below the boiling point and cools what is left. Condensation turns gas to liquid and is its opposite.
◇ FAMILY FREEZE AND MELT
Together, fill an ice tray with water and note the time it goes into the freezer. Check it every half hour and record when it is solid.
At the same time, put one ice cube in a cup of cool tap water and another in warm tap water. Time both melts.
Take turns predicting before each check. Which cup will finish first, and by how many minutes?
Set a glass of ice water on the table during lunch and watch for drops on the outside. Who spots the first drop?
Talk it over: in each test, which way did heat flow, and what did it do to the particles?
For a grown-up
Warm tap water is the warmest thing used today. A grown-up handles any kettle, stove or microwave if hotter water is discussed.
The freezer stays closed between checks so the ice freezes evenly. Nothing from the Bench is eaten or tasted.
This week's facts come from NASA Glenn, the U.S. Geological Survey Water Science School and LibreTexts, at usgs.gov and libretexts.org.
Safety first
Only water goes in the ice tray and the cups. Nothing goes in the mouth.
A grown-up handles any hot water hotter than the tap.
Wipe up drips right away so no one slips, and wash your hands when the tests are done.
THINK IT THROUGH
  • Read the question.
  • Tap your answer.
An ice cube melts faster in warm water than in cool water. Why?
Water in the freezer turns to ice. What is happening to its particles?
Drops appear on the outside of the lunch glass. Where did that water come from?
Water freezes at what temperature in degrees Celsius? Type a number.
WHY THIS EXERCISEYour ice tray reached this temperature today, from the inside out.
Bench Day checkTrue or false?
Heat flowed from the warm water into the ice cube.?
Freezing happens when particles gain energy.?
The drops on the cold glass came from the air.?
Ice melts faster in cool water than in warm water.?
WHY THIS EXERCISEFreeze, melt and condense are the three changes of state your family watched in one day.
Draw your two cups side by side with the melt times written under each. Add arrows showing heat flowing from water into ice.
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