Physical Change
Give two examples of physical changes from everyday life and say why each is physical.
Examples: tearing paper (shape changes, same material); melting chocolate (state changes, same substance). Both are physical because composition unchanged.
A candle burning shows both physical and chemical changes. Describe one physical change and one chemical change that happen when a candle burns.
Physical: wax melts. Chemical: wick burns producing ash and odor; new substances form.
A teacher gives you an unknown solid and asks you to use only physical properties to identify it from a list of possibilities. Name three physical tests you could try in the classroom.
Tests: observe color, measure mass, test solubility in water, check melting point/boiling, measure hardness/texture.
Explain, in terms of particle motion, what happens when water changes from liquid to gas. Use the language from the unit (small particles move differently).
When heated, particles gain energy, move faster, and spread farther apart so liquid becomes gas.
Describe how you could reverse a physical change and give one example where reversal is easy.
Reversible: freezing melted water back to ice. Example: water freezing/melting.
Explain why a new substance being formed is strong evidence for a chemical change (use student-friendly reasoning).
New substances have different properties than the originals; you cannot easily get the original back (irreversible).
Describe how measuring mass in a closed system helps students check whether a chemical change occurred.
In a closed system, mass stays same unless new substances leave/enter; chemical changes rearrange atoms but mass is conserved — students can detect unexpected mass changes only if system is open. (Emphasize closed-system observation.)
A student claims, "Water must boil to become a gas." Explain why this is not always true and give one classroom-observable example.
Water can evaporate (become gas) at temperatures below boiling (e.g., puddles drying), so boiling is not required.
You are given a mixture of sand and iron filings. Describe a student plan (step-by-step) to separate them using simple materials.
Use a magnet to pull out iron filings, then sift/sieve or wash to separate sand — steps: mix, use magnet over paper to collect filings, decant or filter sand.
Design a simple classroom investigation (materials and steps) to test whether mixing two liquids causes a chemical change. Include at least two observable signs you would look for.
Example investigation: mix liquid A and B in small, labeled containers; observe for bubbling, temperature change with thermometer, color change, odor; run control trials; record data. If bubbling + temperature change + new color appear, likely chemical.
Explain how both physical and chemical properties are affected during a chemical change, using rusting iron as an example.
Rusting: physical properties (color, texture) change and chemical composition changes (iron oxides form) — both property types affected.
Create a short argument (2–3 sentences) that shows how temperature causes state changes, including what happens to particle energy and spacing.
"When temperature increases, particle energy increases so particles move faster and spread out, causing liquids to become gases. When temperature decreases, particles slow and come closer, making solids." (Teachers: ensure students reference particle motion/energy.)