AP Chemistry - Chapter 3 Vocabulary: Mass & Stoichiometry

Mass Spectrometer

An instrument used to determine the relative masses of atoms by the deflection of their ions on a magnetic field which are then accelerated and deflected according to their masses

• The lighter they are, the more they get deflected

Atomic Mass/ Weight

The mass of the atom in atomic mass units (amu)

• One atomic mass unit is defined as a mass exactly euqal to 1/12 the mass of one carbon-12 atom

Mole (mol)

The amount of substance that contains as many elementary entities (atoms, molecules, or other particles) as there are atoms in exactly 12 grams (or 0.012 kilograms) of the carbon-12 isotope

Molar Mass

The mass in (grams or kilograms) of 1 mole of units of a substance

Percent Composition

The percent by mass of each element in a compound

Empirical Formula

A formula with the lowest whole-number ratio of elements in a compound

Molecular Formula

A chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound

Chemical Equation

A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products during a chemical reaction

Reactant

A chemical substance that is present at the start of a chemical reaction

Product

A substance formed as a result of a chemical reaction

Stoichiometry

The quantiative study of reactants and products in a chemical reaction

Stoichiometric Quantities

Quantities of reactants mixed in exactly the correct amounts so that all are used up at the same time (determined by the proportions indicated by the balanced equation)

Limiting Reactant/ Reagent

The reactant used up first in a reaction

Excess Reactant/ Reagent

Reactants present in quantities greater than necessary to react with the quantity of the limiting reagent

Theoretical Yeld

The amount of product that would result if all the limiting reagent reacted

Actual/ Experimental Yield

The amount of product actually obtained from a reaction (in a lab environment)

Percent Yield

The proportion of the actual yield to the theoretical yield