Changes Around Us: Physical and Chemical — Science STD 7 — Question

Title: Melting and Freezing Water
Materials:
→ Ice cubes
→ A glass or beaker
→ A heat source (like a stove or a microwave - with adult supervision!) or just a warm environment
→ A freezer
Procedure:
1. Melting:
→ Place an ice cube in the glass or beaker.
→ Leave the glass at room temperature or gently heat it (with adult supervision) until the ice cube melts into liquid water.
→ Observe the change. The solid ice turns into liquid water.
2. Freezing:
→ Place the glass of liquid water in the freezer.
→ Leave it in the freezer for a few hours until the water freezes and turns back into solid ice.
→ Observe the change. The liquid water turns back into solid ice.
Explanation:
→ Melting is a physical change where solid ice changes into liquid water when heat is applied.
→ Freezing is also a physical change where liquid water changes back into solid ice when the temperature is lowered.
→ This experiment demonstrates a reversible change because the water changes its state (solid to liquid and back), but it's still water. No new substance is formed.