Chemistry · Grades 9–12
Carbon chemistry and system accounting
Track carbon atoms across reservoirs without treating transfers as disappearance.
Learn the idea
Reservoirs
Carbon occurs in air, water, living matter, soils and rocks in different chemical forms.
Transfer
A chemical or biological process can transfer carbon between reservoirs while conserving atoms.
Combustion model
Complete combustion of a hydrocarbon forms carbon dioxide and water in a simplified oxygen-sufficient model.
Boundary
A local decrease in one reservoir is not automatically a global removal.
Worked examples
When carbon moves from a fuel to carbon dioxide, what is conserved in the chemical model?
Chemical reactions rearrange atoms.
The carbon atoms.
One molecule of propane C₃H₈ undergoes complete combustion in the stated model. How many CO₂ molecules contain its carbon?
Each propane molecule has three carbon atoms, each going to one CO₂ molecule.
3
Check your understanding
What is wrong with saying a carbon-containing waste vanished because it was burned?
- Its atoms are redistributed into products.
- Chemical reactions destroy all nuclei.
- Gas products have no matter.
Why is a system boundary important in a carbon balance?
A model reservoir gains 14 units of carbon and loses 9 units. What is its net change?
Answers and marking notes
Answers and marking notes
- Its atoms are redistributed into products.
Mass and atom accounting include gaseous products.
- A transfer out of one chosen system may enter another rather than leave the global environment.
Specify inputs, outputs and storage.
- 5
14 − 9 = +5 units.
Further reading and review references
These are reference links, not copied exercises, institutional endorsement or proof of independent review.
Independent educational review required. Grade bands are approximate; these are not officially aligned curricula.