⚗️ Stoichiometry
1 mole = 6.022 × 10²³ particles = molar mass in grams
The Mole — Three Equivalent Statements
Everything you need to know about a mole in one mnemonic
Avogadro's number: 6.022 × 10²³. One mole of any substance has this many particles AND has a mass equal to its molar mass in grams. 1 mol H₂O = 6.022×10²³ molecules = 18g.
⚗️ Stoichiometry
Mole Map: g ↔ mol ↔ particles
Mole Conversion Steps
The mole map — convert between grams, moles, and particles
Grams ÷ molar mass = moles. Moles × 6.022×10²³ = particles. Particles ÷ 6.022×10²³ = moles. Moles × molar mass = grams. Always go through moles as the middle step.
⚗️ Stoichiometry
Limiting reagent = runs out first
Limiting Reagent
The limiting reagent stops the reaction — find it first
Divide each reactant's moles by its stoichiometric coefficient. The smallest result is the limiting reagent. Base all product calculations on the limiting reagent, not the excess.
⚗️ Stoichiometry
% Yield = (actual ÷ theoretical) × 100
Percent Yield Formula
Percent yield — how efficient was your reaction?
Actual yield is what you actually got in the lab. Theoretical yield is what stoichiometry predicts. Divide actual by theoretical, multiply by 100. Can never exceed 100%.
⚗️ Stoichiometry
STP: 0°C and 1 atm, 1 mol gas = 22.4 L
Standard Temperature and Pressure
At STP, one mole of any gas occupies 22.4 liters
Standard Temperature and Pressure = 0°C (273.15 K) and 1 atmosphere. At these conditions, the molar volume of any ideal gas is 22.4 L/mol. Essential for gas stoichiometry problems.
Calculating Molar Mass
Molar mass = sum of atomic masses from periodic table. 1 mol H₂O = 18.02 g/mol
Calculating Molar Mass
How to find the mass of one mole of any compound
Add up the atomic masses of all atoms in the formula. H₂O: 2(1.008) + 16.00 = 18.02 g/mol. CO₂: 12.01 + 2(16.00) = 44.01 g/mol. This number converts between grams and moles. Memorize: H≈1, C≈12, N≈14, O≈16, Na≈23, Cl≈35.5.
Percent Composition
Percent composition: (mass of element ÷ molar mass of compound) × 100
Percent Composition
What fraction of a compound's mass comes from each element
Find the molar mass. Divide each element's total mass by the molar mass. Multiply by 100. Example: H₂O is 11.2% H and 88.8% O. Used to verify empirical formulas and analyze unknown compounds.
Empirical vs Molecular Formula
Empirical formula = simplest whole-number ratio. Molecular = actual number of atoms.
Empirical vs Molecular Formula
The simplest ratio vs the actual formula
Empirical formula of glucose (C₆H₁₂O₆) is CH₂O — divide all subscripts by 6. To find molecular formula from empirical: divide molar mass by empirical formula mass → multiply all subscripts by that factor. Benzene C₆H₆ has empirical formula CH.
Yield Calculations
Theoretical yield = what stoichiometry predicts. Actual yield = what you really get. % yield = actual/theoretical × 100
Yield Calculations
Why reactions never give you 100% of the expected product
Reactions never reach perfect completion. Side reactions, incomplete reactions, product loss during transfer all reduce actual yield. % yield = (actual yield ÷ theoretical yield) × 100. A yield of 80-90% is considered good in practice.
Dimensional Analysis
Dimensional analysis: multiply by conversion factors until unwanted units cancel
Dimensional Analysis
The systematic way to convert between units in stoichiometry
Write what you have. Multiply by a fraction that cancels the unwanted unit and introduces the desired unit. Keep going until you reach the target unit. Grams → moles: multiply by (1 mol / molar mass). Moles → particles: multiply by (6.022×10²³ / 1 mol).
Molarity
Concentration (molarity) = moles of solute ÷ liters of solution. M = mol/L
Molarity
The most common way to express solution concentration in chemistry
M = n/V. To make a 1 M NaCl solution: dissolve 1 mole (58.44 g) of NaCl in enough water to make 1 liter total. Dilution formula: M₁V₁ = M₂V₂ — moles of solute don't change when you add more water.
Gas Stoichiometry
Gas stoichiometry: at STP, use 22.4 L/mol. Otherwise use ideal gas law PV = nRT
Gas Stoichiometry
Converting between moles and volume of gases
At STP (0°C, 1 atm): 1 mol of any ideal gas = 22.4 L. Use this as a conversion factor: (22.4 L / 1 mol). For non-STP conditions, use PV = nRT where R = 0.08206 L·atm/mol·K. Always convert temperature to Kelvin.