Grade 10 · Chemical Reactions and Conservation of Mass · Chemical Equations
Balancing Chemical Equations
Making the atoms on both sides match.
Learning objectives
- Write word and symbol equations.
- Balance simple chemical equations.
- Explain what coefficients represent.
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.
HS-PS1-2
Construct and revise an explanation for the outcome of a simple chemical reaction based on the outermost electron states of atoms, trends in the periodic table, and knowledge of the patterns of chemical properties.
MYP criteria
- Criterion A — Knowing and Understanding
ENGAGE
Counting atoms like an accountant
EXPLAIN
How to balance
- Write the correct formulas for reactants and products.
- Count each type of atom on both sides.
- Adjust coefficients (the big numbers in front) only.
- Recount until every element matches.
Example: CH4 + 2O2 gives CO2 + 2H2O. Carbon 1 = 1, hydrogen 4 = 4, oxygen 4 = 4.
Interactive simulation · PhET
Balancing Chemical Equations
Balance each equation, then use the bar charts to check both sides.
While you explore
- How do you know an equation is balanced?
- Why can you change coefficients but never subscripts?
Practice questions
0/1 correct
Level 1
Balance: H2 + O2 gives H2O. What are the correct coefficients?
Reflect & track
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