Coefficient — Science definition

Defined in 2 courses:

Where it is taught

In use

A coefficient, on the other hand, just says how many of that same molecule you have — like writing a '3' in front of a recipe to make three identical batches.

Balancing Chemical Equations

A coefficient, by contrast, just says 'how many' of that exact substance you have, the way a '3' in front of a recipe means three identical batches.

Balancing Chemical Equations

Questions using coefficient

Problem 1

Balance counts by changing whole-particle coefficientsBalance counts by changing whole-particle coefficientsUnbalanced: H₂ + O₂ → H₂OLeft: H 2, O 2. Right: H 2, O 1.Balanced: 2H₂ + O₂ → 2H₂OLeft: H 4, O 2. Right: H 4, O 2.A coefficient counts whole molecules. Changing H₂O to H₂O₂ changes identity.
The first specified water equation has unequal oxygen counts. The balanced form uses coefficients 2, 1 and 2 to preserve four H atoms and two O atoms. Subscripts remain unchanged because they describe each substance. An equation arrow describes the chemical account; it is not a physical force or motion arrow.
For this unit’s illustrated case, why must adding 2 before H₂O also be followed by changing the H₂ coefficient?
Answer and explanation

Two H₂O molecules contain four H atoms, so two H₂ reactant molecules are needed to match them. The O₂ molecule already supplies the two O atoms.

A coefficient multiplies every atom in a formula. Recount all elements after each change, including an element that was previously balanced. This prevents solving the oxygen mismatch by accidentally creating a hydrogen mismatch.

Two H₂O molecules contain four H atoms, so two H₂ reactant molecules are needed to match them. The O₂ molecule already supplies the two O atoms.

Response criteria

  • Use the named labels, directions or supplied quantities accurately.
  • Connect the visual evidence to the scientific mechanism or calculation.
  • State the relevant model conditions or limitation.

Problem 2

Balance: __CH₄ + 2O₂ → CO₂ + 2H₂O. What coefficient goes before CH₄?
Answer and explanation

1

One methane supplies one carbon and four hydrogens, matching CO₂ and 2H₂O.

Problem 3

Balance: 2Mg + O₂ → __MgO. What coefficient goes before MgO?
Answer and explanation

2

Two magnesium atoms and two oxygen atoms give 2MgO.

Problem 4

Balance the decomposition ___KClO₃ → ___KCl + ___O₂. What coefficient belongs in front of O₂?
Answer and explanation

3

2KClO₃ → 2KCl + 3O₂ balances: K 2 = 2, Cl 2 = 2, O 6 = 6. The coefficient on O₂ is 3.

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