# Chapter 3 Vocabulary

 Stoichiometry
 The relationships among the quantities of reactants and products involved in chemical reactions.
 Law of Conservation of Mass
 Total mass of products of chemical reaction are the same mass of reactants, so that mass remains constant during the reaction.
 Chemical Equation
 A representation of a chemical reaction using the chemical formulas of the reactants and products – balanced contain numbers of atoms of each element on both side.
 Reactant
 A starting substance in a chemical reaction – appears to the left of the arrow in a chemical reaction.
 Product
 A substance produced in a chemical reaction – appears to the right of the arrow in a chemical reaction.
 Combustion Reaction
 Chemical reaction that proceeds with evolution of heat and usually a flame – most involve a reaction with oxygen, as in burning of a match.
 Combination Reaction
 Chemical reaction in which two or more substances combine to form a single product.
 Decomposition Reaction
 Chemical reaction in which a single compound reacts to give two or more products.
 Atomic Weight
 Average mass of atoms in an element in amu – numerically equal to mass in grams of 1 mol of the substance.
 Atomic Mass Unit(amu)
 Unit based on value of exactly 12 amu for the mass of the isotope of carbon that has 6 protons and 6 neutrons in the nucleus.
 Formula Weight
 Mass of a collection of atoms represented by a chemical formula. (IONIC)
 Molecular Weight
 Mass of a collection of atoms represented by the chemical formula for a molecule. (COVALENT)
 Mass Spectrometer
 An instrument used to measure the precise masses and relative amounts of atomic and molecular ions.
 Mole
 A collection of Avagadro’s Number of objects.
 The number of Carbon atoms in exactly 12g of Carbon 12. Equals 6.022 x 1023.
 Molar Mass
 The mass of 1 mol of a substance in grams – numerically equal to the formula weight in amu.
 Limiting Reactant
 Reactant present in the smallest stoichiometric quantity in a mixture of reactants – amount of product that can form is constrained by complete consumption of this reactant.
 Theoretical Yield
 Quantity of a product that is calculated to form when all of the limiting reagent reacts.
 Percent Yield
 The ratio of the actual (experimental) yield of a product to its theoretical (calculated) yeild, multiplied by 100.