Glossary
Avogadro's Number
The number of particles (atoms, molecules, ions, etc.) in one mole of a substance, approximately 6.022 x 10^23.
Example:
If you have 1 mole of gold, you have 6.022 x 10^23 gold atoms, which is Avogadro's Number of atoms.
Balanced Chemical Equation
A chemical equation where the number of atoms for each element and the total charge are the same for both the reactants and the products.
Example:
The reaction 2H₂ + O₂ → 2H₂O is a balanced chemical equation because there are 4 hydrogen atoms and 2 oxygen atoms on both sides.
Dimensional Analysis
A problem-solving method that uses conversion factors to systematically change units, ensuring that calculations are set up correctly and units cancel out appropriately.
Example:
Converting grams to moles by multiplying by (1 mol / molar mass) is a common application of dimensional analysis in stoichiometry.
Molar Mass
The mass in grams of one mole of a substance, numerically equivalent to its atomic or molecular weight in atomic mass units (amu).
Example:
The molar mass of CO₂ is approximately 44.01 g/mol, meaning 44.01 grams of CO₂ contains one mole of CO₂ molecules.
Molar Volume
The volume occupied by one mole of any gas at Standard Temperature and Pressure (STP), which is 22.4 liters.
Example:
At STP, 1 mole of helium gas and 1 mole of oxygen gas both occupy a molar volume of 22.4 L.
Mole (mol)
The SI unit for the amount of substance, defined as the amount of substance that contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.
Example:
A mole of water molecules contains 6.022 x 10^23 H₂O molecules, regardless of its mass.
Mole Ratios
Conversion factors derived from the stoichiometric coefficients in a balanced chemical equation, used to relate the moles of one substance to the moles of another.
Example:
In the reaction N₂ + 3H₂ → 2NH₃, the mole ratio between N₂ and NH₃ is 1:2.
STP (Standard Temperature and Pressure)
A set of standard conditions for experimental measurements, defined as 0°C (273.15 K) and 1 atmosphere (101.325 kPa) of pressure.
Example:
When discussing gas volumes, STP provides a common reference point, allowing for direct comparison of gas quantities.
Stoichiometric Coefficients
The numbers placed in front of chemical formulas in a balanced chemical equation, indicating the relative number of moles of each reactant and product.
Example:
In 2Na + Cl₂ → 2NaCl, the stoichiometric coefficients are 2 for Na, 1 for Cl₂, and 2 for NaCl.
Stoichiometry
The quantitative study of chemical reactions, focusing on the relationships between the amounts of reactants consumed and products formed.
Example:
Using stoichiometry, a chemist can calculate exactly how much oxygen is needed to completely burn a certain amount of methane.