Topic 6 Stoichiometry

What is an atomic mass unit (amu)?

A unit of mass used to express atomic and molecular weights.

What is the average atomic mass?

The weighted average of the atomic masses of an element's isotopes.

Define a mole in chemistry.

A unit defined as the amount of substance that contains the same number of entities as there are in 12 grams of carbon-12.

What is Avogadro's number?

The number of particles in one mole of a substance.

What does molar mass represent?

The mass of one mole of a substance in grams per mole (g/mol).

What is the definition of percentage composition?

The percentage by mass of each element in a compound.

Define empirical formula.

Consists of element symbols with subscripts indicating the smallest whole-number ratio of different atoms.

What is a molecular formula?

Indicates the actual number of atoms of each element in a molecule of a substance.

What is stoichiometry?

The study of the mass relationships between reactants and products in chemical reactions.

What is a mole ratio?

A conversion factor for mole relationships derived from balanced equations.

Define limiting reactant.

The reactant that is used up first and limits product formation in a chemical reaction.

What is an excess reactant?

The reactant that remains after the reaction has completed.

What is the theoretical yield?

The maximum amount of product that can be formed from given reactants under ideal conditions.

Define actual yield.

The measured amount of a product obtained from a chemical reaction.

What is percentage yield?

The ratio of actual yield to theoretical yield, expressed as a percentage.

How is molar mass defined?

Number of grams per one mole of a substance.

What is relative atomic mass?

Atomic masses are expressed in relative atomic mass units (amu).

How is the average atomic mass determined?

A weighted average of an element's isotopes, found on the periodic table.

What is the significance of 6.022 x 10^23 in chemistry?

It is Avogadro's number, representing the number of particles in one mole of a substance.

What does an empirical formula represent?

The smallest whole number ratio of different atoms in a compound.

What are the four problem types in stoichiometry?

Amounts in moles, moles to grams, grams to moles, and grams to grams via moles.

How do you identify limiting and excess reactants?

Determine which reactant is used up first and which remains after the reaction completes.

What is the formula to calculate percentage yield?

Percentage yield = (actual yield / theoretical yield) x 100%.