AM-03.05 — Chemical reaction and conservation

Course compass

Guiding question: Why must a chemical equation count the same number of each atom before and after?

Markers: 📏 MEASURED · 📐 CONVENTION · 🧮 CALCULATED · 🎓 TEACHING ASSUMPTION · ⚠️ APPROXIMATION

define reactant and product
balance by counting
respect conservation
distinguish equation from process

Open educational resource: this content is not professional training, a diploma, certification, or authorization. Examples teach principles and do not replace engineering, testing, or qualification of a real system.

1 — A reaction rearranges bonds

Starting substances are reactants; formed substances are products. Atoms are rearranged among molecules.

The equation must conserve each element in the chemical model.

Teaching diagram 1: 1 — A reaction rearranges bonds — 1 — A reaction rearranges bonds

2 — Balance with coefficients

For water formation, H₂ + O₂ → H₂O does not conserve O.

2 H₂ + O₂ → 2 H₂O counts 4 H and 2 O on both sides.

Teaching diagram 2: 2 — Balance with coefficients — 2 — Balance with coefficients

3 — Conservation becomes a calculation tool

Once coefficients are balanced, they give ratios of molecule counts or moles.

Real mass calculations then require molar masses, taught elsewhere.

Teaching diagram 3: 3 — Conservation becomes a calculation tool — 3 — Conservation becomes a calculation tool

4 — Chemical equation ≠ industrial process

A reaction written on paper does not by itself specify temperature, catalyst, kinetics, efficiency, safety, or equipment.

Space Academy teaches stoichiometric logic before process engineering.

Teaching diagram 4: 4 — Chemical equation ≠ industrial process — 4 — Chemical equation ≠ industrial process

Three complete examples: change one assumption to understand

Before each calculation, identify where every number comes from and whether it is measured, conventional, assumed, or calculated.

Three numerical examples in the course — Three compared cases

Example A — unbalanced

H₂ + O₂ → H₂O: left H=2,O=2; right H=2,O=1.

O is not conserved; the equation must be corrected.

Example B — balanced

2 H₂ + O₂ → 2 H₂O: left H=4,O=2; right H=4,O=2.

Counts match.

Example C — scale up

4 H₂ + 2 O₂ → 4 H₂O is also balanced: all coefficients doubled.

Same chemical proportion, doubled scale.

Inverse calculation

If 6 H₂ molecules react in a 2:1 ratio with O₂, the stoichiometric count requires 6/2=3 corresponding O₂ units.

Common trap and result check

Trap: believing a balanced equation proves a reaction will be fast, complete, or easy to implement.

Check units, sign, order of magnitude, and consistency with a limiting case.

Exercises and answers

Restate

Explain in your own words what the equation connects.

Answer: A correct answer says what changes, in which direction, and why.

Vary

Halve one input and predict the result before calculating.

Answer: Qualitative prediction comes before calculation.

Check

What independent check can you perform?

Answer: Units, inverse substitution, a physical bound, or comparison with a simple case.

AM-03.05 — Chemical reaction and conservation: atoms rearrange; they do not vanish