Stoichiometry Terms

Actual Yield

When a chemical reaction is completed, this is the amount of product that you actually make (the amount of stuff you can weigh).

Atomic Mass

The mass of an atom expressed in atomic mass units (amu).

Avogadro's Number

A number equal to 6.023 × 1023. It is also equal to the number of atoms or molecules in one mole of a substance.

Chemical Equation

A chemical equation is a representation of a chemical reaction where the reactants are given on the left hand side of an arrow followed by the products of a reaction on the right hand side.

Chemical Reaction

In a chemical reaction, a chemical change must occur; the hallmark of any chemical reaction is the creation of a new substance. Physical changes can also occur during a chemical reaction.


Variant of a chemical element that has the same number of protons, but different numbers of neutrons.

Law of Conservation of Mass

A scientific principle that states that matter cannot be created nor destroyed.

Limiting Reagent

The limiting reagent is the chemical in a reaction that determines how far a reaction can proceed or how much product a reaction can make.


Visible to the naked, or unaided, eye.


Extremely small; visible with a microscope.

Molar Mass

The mass in one mole of a substance.


A measurement of an amount of a substance, always equal to 6.023 × 1023 units.


A group of atoms that are held together by covalent bonds.

Percent Composition

The percentage by mass of each element in a compound.

Percent Yield

The actual yield of a chemical reaction divided by the theoretical yield times 100%.

Physical State

The state of the matter: solid, liquid, or gas.


A molecule that is produced in a chemical reaction. Products are generated by reactants.


The chemicals that are present before a chemical reaction takes place. They react together to produce new chemical compounds. In a chemical equation, reactants are listed on the left hand side of the arrow.


The set proportions in which elements or compounds react with one another.

Theoretical Yield

The quantity of product obtained from the complete conversion of the limiting reagent in a chemical reaction. This is how much product a reaction would give us if we lived in a perfect world and no errors were allowed.

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