Chemical reactions · Topic 8 of 15

The Mole & Stoichiometry

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Chemistry · the mole

A mole is 6.02 × 10²³ particles; molar mass turns grams into moles, and a balanced equation's coefficients give the mole ratio.

01 · Avogadro1 mol = 6.02 × 10²³ particles

02 · Molar massMolar mass = grams per mole (g/mol)

03 · Mole ratioCoefficients give the mole ratio

Molar mass = grams in 1 mole (same number as the atomic mass) must know

1 mol of anything has the same count of particles, not the same mass

Balanced coefficients = mole ratio (2H₂ : 1O₂ : 2H₂O) must know

Grams → moles → mole ratio → moles → grams must know

Balance the equation before using its mole ratio

1 mole = 6.02 × 10²³ particles (Avogadro's number) must know

Compound molar mass = sum of atomic masses × subscripts (NH₃ = 17.0 g/mol)

moles = grams ÷ molar mass; grams = moles × molar mass

particles = moles × 6.02 × 10²³

66.0 g CO₂ ÷ 44.0 g/mol = 1.50 mol

0.50 mol × 6.02 × 10²³ = 3.01 × 10²³ molecules

2.0 mol CH₄ needs 4.0 mol O₂ = 4.0 × 32.0 g = 128 g O₂

The mole ratio is never a gram ratio (convert grams to moles first)

Show 2 more facts

Factor-label method: write units and let them cancel

Exact Avogadro constant: 6.02214076 × 10²³ /mol

Pearl

Grams to moles, moles to moles, moles to grams: the mole ratio only ever works in moles.

Practice this topic, then test the whole section.

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