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Lesson 19: Conservation of Mass (Physical Changes) Mass before and after change Closed vs open systems Simple experiments
Year 8 • Chemistry
Conservation of Mass (Physical Changes)
In this lesson, students explore the conservation of mass during physical changes, compare open and closed systems, and understand why mass stays the same before and after a change.
Lesson Objectives
- Understand conservation of mass.
- Explain mass before and after physical changes.
- Compare open and closed systems.
- Describe simple experiments showing conservation of mass.
1. What Is Conservation of Mass?
The law of conservation of mass states that mass is never created or destroyed.
It stays the same during physical changes.
[ Image Placeholder – Conservation of Mass Diagram ]
Key idea:
• Mass before change = mass after change
• Mass before change = mass after change
2. Physical Changes and Mass
A physical change does not create a new substance.
The material only changes form or state.
[ Image Placeholder – Melting Ice ]
Examples:
• Ice melting into water
• Water freezing into ice
• Sugar dissolving in water
• Ice melting into water
• Water freezing into ice
• Sugar dissolving in water
Even though the appearance changes, the mass stays the same.
3. Open vs Closed Systems
Mass measurements depend on whether the system is open or closed.
[ Image Placeholder – Open vs Closed System ]
Closed system:
• Nothing can escape
• Mass stays the same
• Nothing can escape
• Mass stays the same
Open system:
• Gas or liquid can escape
• Measured mass may change
4. Simple Experiments
Experiments help us test conservation of mass.
[ Image Placeholder – Balloon Experiment ]
Examples:
• Ice melting in a sealed container
• Dissolving salt in water with lid on
• Vinegar and baking soda in a closed bag
• Ice melting in a sealed container
• Dissolving salt in water with lid on
• Vinegar and baking soda in a closed bag
Practice Questions
A. Fill in the Blanks
- Mass is never __________ or destroyed.
- Physical changes do not form __________ substances.
- In a closed system, mass stays the __________.
- Melting is a __________ change.
- Gas can escape from an __________ system.
B. True or False
- Mass changes when ice melts.
- Conservation of mass applies to physical changes.
- A closed system prevents mass loss.
- Dissolving sugar creates a new substance.
- Open systems may show mass loss.
C. Short Answer
- What does conservation of mass mean?
- Give one example of a physical change.
- Why might mass seem to decrease in an open system?
- What is a closed system?
- How can experiments show conservation of mass?
✅ Show Answer Key
A. Fill in the Blanks
- created
- new
- same
- physical
- open
B. True or False
- False
- True
- True
- False
- True
C. Short Answer
- Mass stays the same before and after a change.
- Melting ice / dissolving sugar.
- Because gas or liquid escapes.
- A system where nothing can escape.
- By measuring mass before and after changes.
© Aviate Learning – Conservation of Mass (Year 8)
⚖️ Interactive Conservation of Mass Simulator
Choose a system type and observe how the mass changes during a physical change.
Mass Before: 100 g
Mass After: ?
Choose a system and start the physical change.