Mole Concept Speed Pack

The mole triangle

n = mass / molar mass = particles / N_A = volume of gas at STP / 22.4 L (use 22.7 L at SATP/IUPAC 1 bar if the question says so). N_A = 6.022 × 10²³ mol⁻¹.

Limiting reagent in two steps

1. Divide moles of each reactant by its coefficient.
2. Smallest value = limiting reagent.

Example: N₂ + 3H₂ → 2NH₃, with 2 mol N₂ and 3 mol H₂: 2/1 = 2, 3/3 = 1 → H₂ limits; NH₃ formed = 2 mol.

Concentration terms

Term	Formula	Temperature dependent?
Molarity (M)	mol solute / L solution	Yes
Molality (m)	mol solute / kg solvent	No
Mole fraction	ni / ntotal	No

Empirical formula shortcut

% → divide by atomic mass → divide by smallest → multiply to whole numbers. Example: C 40%, H 6.7%, O 53.3% → 3.33 : 6.7 : 3.33 → CH₂O.

Percentage yield

% yield = (actual / theoretical) × 100.

Traps

• Using molarity when the question gives kg of solvent.
• Forgetting coefficients when finding limiting reagent.

Related pathway: EkoDemy JEE and NEET Class 11 Chemistry.

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