Molar Mass & Stoichiometry – Key Vocabulary

Vocabulary flashcards summarizing essential terms and definitions from lecture notes on molar mass, stoichiometry, limiting reactants, yields, and reaction energetics.

Molar Mass

Mass (in grams) of one mole of a substance; numerically equals the atomic or formula mass and is rounded to the nearest 0.1 g in this text.

Mole (mol)

SI unit representing 6.02 × 10^23 particles (atoms, molecules, ions, or formula units) of a substance.

Avogadro’s Number

6.02 × 10^23 particles per mole; links microscopic particles to macroscopic amounts.

Law of Conservation of Mass

Principle stating matter is neither created nor destroyed; total mass of reactants equals total mass of products in a chemical reaction.

Balanced Chemical Equation

Chemical statement with equal numbers of each type of atom on both sides, providing mole ratios for reactants and products.

Stoichiometry

Quantitative study of the relationships between amounts of reactants and products in a balanced chemical equation.

Stoichiometric Coefficient

Whole-number multiplier in a balanced equation indicating the relative moles of each substance.

Mole–Mole Factor

Ratio of coefficients from a balanced equation used to convert between moles of two substances.

Conversion Factor (from Molar Mass)

Equality that relates grams and moles of a substance (e.g., 1 mol CH4 = 16.0 g CH4).

Mass-to-Mole Calculation

Problem type converting grams of a substance to moles using its molar mass.

Mass-to-Mass Calculation

Stoichiometric conversion that begins with grams of a reactant and yields grams of product via molar mass and mole–mole factors.

Limiting Reactant

Reactant that is completely consumed first, limiting the amount of product formed.

Excess Reactant

Reactant present in a quantity greater than needed; remains after the reaction is complete.

Theoretical Yield

Maximum possible amount of product predicted by stoichiometry, assuming complete conversion of limiting reactant.

Actual Yield

Measured amount of product obtained from an experiment or industrial process.

Percent Yield

Ratio of actual yield to theoretical yield × 100%; measures reaction efficiency.

Percent Yield Formula

Percent Yield = (Actual Yield / Theoretical Yield) × 100%.

Activation Energy (Ea)

Minimum energy required for reactant molecules to collide effectively and form products.

Collision Theory – Conditions

For reaction: (1) molecules must collide, (2) proper orientation, (3) sufficient energy (Ea).

Heat of Reaction (ΔH)

Enthalpy change; heat absorbed or released, calculated as ΔH = Hproducts – Hreactants.

Exothermic Reaction

Reaction that releases heat; products have lower energy than reactants; ΔH is negative.

Endothermic Reaction

Reaction that absorbs heat; products have higher energy than reactants; ΔH is positive.

Steps to Calculate Molar Mass

(1) Obtain each element’s molar mass, (2) multiply by subscripts, (3) sum the results.

Steps for Grams ↔ Moles Conversion

State quantities, plan path, use molar mass as conversion factor, set up & solve.

Product Method (Limiting Reactant)

Compute product amount from each reactant; the one producing the least product is limiting.

Reactant Method (Limiting Reactant)

Assume one reactant is limiting, calculate required amount of the other; insufficient supply identifies the true limiting reactant.

Shortcut Method (Limiting Reactant)

Divide moles of each reactant by its coefficient; smallest resulting value indicates the limiting reactant.

Mole Ratio

Proportional relationship of moles between any two species in a balanced equation (same as mole–mole factor).