7 Chemical Reactions and Stoichiometry - Vocabulary Flashcards

Vocabulary flashcards covering key concepts from the notes on atomic mass, isotopes, Avogadro’s number, the mole, molar mass, and stoichiometry.

Atomic Mass

The mass of a single atom, usually expressed in amu, representing the average mass of an element’s isotopes weighted by natural abundance; 1 amu = 1/12 the mass of a C-12 atom; 1 amu ≈ 1.66054×10^-27 kg.

Atomic Mass Unit (amu) / Dalton (Da)

Units of mass equal to 1/12 the mass of a C-12 atom; 1 amu = 1 Da; used interchangeably and based on carbon-12.

Isotope

Atoms of the same element with different numbers of neutrons, leading to different atomic masses.

Mass Number

Total number of protons and neutrons in an atom; always a whole number.

Protons

Positively charged particles in the nucleus with a mass of about 1.0073 amu.

Neutrons

Electrically neutral particles in the nucleus with a mass of about 1.0087 amu.

Electrons

Negligible mass (~0.00055 amu) compared to protons/neutrons; mass is usually ignored in atomic mass calculations.

Atomic Mass vs Mass Number

Atomic mass is the weighted average of isotopes; mass number is the total number of protons and neutrons and is an integer.

Weighted Average (Isotopic Masses)

The atomic mass obtained by summing each isotope’s mass multiplied by its natural abundance.

Mass Spectrometer

Instrument that measures isotope masses and abundances by ionizing atoms, accelerating them, deflecting with a magnetic field, and detecting mass-to-charge ratios.

m/z (Mass-to-Charge Ratio)

Ratio used in mass spectrometry to identify ions by their mass divided by their charge.

Isotope Abundance

The relative amount or percentage of a given isotope in nature.

Molecular Mass (Molecular Weight)

Sum of the atomic masses of all atoms in a molecule; expressed in amu or Da.

Calculation of Molecular Mass

Identify formula, find atomic masses, multiply by the number of each atom, and sum.

Molar Mass

Mass of one mole of a substance, in g/mol; numerically equal to the molecule’s molecular mass in amu.

Molecular Mass vs Molar Mass

Molecular mass is in amu; molar mass is in g/mol; both numerically reflect the same composition (1 amu ≈ 1 g/mol per mole).

Avogadro’s Number (NA)

6.022×10^23; the number of particles in one mole, linking atomic scale to macroscopic quantities.

The Mole (mol)

A unit that represents 6.022×10^23 particles (atoms, molecules, or ions).

Determination of Avogadro’s Number

Estimated through X-ray crystallography, Faraday’s constant (electrolysis), and gas laws.

Molar Volume at STP

At STP (0°C, 1 atm), 1 mole of any ideal gas occupies 22.4 L.

PV = nRT

Ideal gas law relating pressure, volume, amount of substance (moles), gas constant, and temperature.

Gas Constant (R)

R = 0.0821 L·atm/(mol·K) in the PV = nRT equation.

Stoichiometry

Calculation of reactant and product amounts using mole ratios from a balanced equation.

Empirical Formula

The simplest whole-number ratio of elements in a compound.

Molecular Formula

The actual number of atoms of each element in a molecule; may be the same as or a multiple of the empirical formula.

Molar Mass of Water (H2O)

2.016 g/mol from H (1.008×2) plus 16.00 g/mol from O; total 18.016 g/mol.

Molar Mass of CO2

12.01 g/mol for C plus 2×16.00 g/mol for O, total 44.01 g/mol.

Carbon-14 Dating

Radiocarbon dating using the decay of C-14 to estimate the age of fossils and artifacts.

Haber Process (Stoichiometry Example)

N2 + 3H2 → 2NH3; illustrates mole ratios and how much reactant is needed to produce a desired amount of product.

Formula Unit

The basic unit of an ionic compound; one mole contains 6.022×10^23 formula units.

Mole-to-Particles Relationship

1 mole corresponds to 6.022×10^23 particles, whether atoms, molecules, or formula units.

STP (Standard Conditions)

0°C and 1 atm; standard reference conditions for gas calculations.