Grade 10 · Chemical Reactions and Conservation of Mass · Conservation of Mass
Conservation of Mass
Why mass never disappears in a chemical reaction.
Learning objectives
- State the law of conservation of mass.
- Use atom counting to show mass is conserved.
- Explain apparent mass changes in open systems.
NGSS alignment
HS-PS1-7
Use mathematical representations to support the claim that atoms, and therefore mass, are conserved during a chemical reaction.
MS-PS1-5
Develop and use a model to describe how the total number of atoms does not change in a chemical reaction and thus mass is conserved.
MS-PS1-2
Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MYP criteria
- Criterion A — Knowing and Understanding
- Criterion C — Processing and Evaluating
ENGAGE
The disappearing mass
EXPLAIN
Atoms are only rearranged
In a chemical reaction atoms are rearranged, never created or destroyed. In a closed system the total mass is unchanged.
Open systems
A burning candle loses mass because carbon dioxide and water vapour escape into the room. Collect them and the mass is conserved.
Interactive simulation · PhET
Reactants, Products and Leftovers
Run a reaction and record what is left over.
While you explore
- Where does the mass of the leftovers go?
- How does this show mass is conserved?
Key vocabulary
- Closed system
- A container where nothing can get in or out.
Practice questions
0/1 correct
Level 1
Why does the mass appear to decrease when a candle burns in the open air?
Reflect & track
Your learning log
Saved privately in this browser — no account needed.
How confident do you feel?