Chapter 14

The Mole, Avogadro's Number, and Molecular Mass

Atomic Mass Unit, U By international agreement, the reference element is chosen to be the most abundant type of carbon, called carbon-12, and its atomic mass is defined to be exactly twelve atomic mass units, or 12 u.

Molecular Mass The molecular mass of a molecule is the sum of the atomic masses of its atoms. For instance, hydrogen and oxygen have atomic masses of 1.007 94 u and 15.9994 u, respectively. The molecular mass of a water molecule (H2O) is: 2(1.007 94 u) + 15.9994 u = 18.0153 u.

Avogadro's Number NA The number of atoms per mole is known as Avogadro's number NA, after the Italian scientist Amedeo Avogadro (1776–1856):

Number of Moles, n The number of moles n contained in any sample is the number of particles N in the sample divided by the number of particles per mole NA (Avogadro's number): The number of moles contained in a sample can also be found from its mass.

Pressure KEY UNITS AT SEA LEVEL 101.325 kPa (kilopascal) 1 atm 760 mm Hg 760 torr 14.7 psi

Standard Temperature & Pressure STP Standard Temperature & Pressure 0°C 273 K 1 atm 101.325 kPa -OR-

A. Boyle’s Law P V PV = k

A. Boyle’s Law The pressure and volume of a gas are inversely related at constant mass & temp P V P1V1 = P2V2

B. Charles’ Law V T

B. Charles’ Law The volume and absolute temperature (K) of a gas are directly related at constant mass & pressure V T V1/T1 = V2/T2

C. Gay-Lussac’s Law P T

P1/T1 = P2/T2 C. Gay-Lussac’s Law The pressure and absolute temperature (K) of a gas are directly related at constant mass & volume P T P1/T1 = P2/T2

D. Avogadro’s Principle

D. Avogadro’s Principle Equal volumes of gases contain equal numbers of moles at constant temp & pressure true for any gas V n

UNIVERSAL GAS CONSTANT Ideal Gas Law PV nT V n PV T = k = R UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK R=8.315 J/molK

UNIVERSAL GAS CONSTANT Ideal Gas Law PV=nRT UNIVERSAL GAS CONSTANT R=0.0821 Latm/molK R=8.315 J/molK

The Ideal Gas Law An ideal gas is an idealized model for real gases that have sufficiently low densities. The condition of low density means that the molecules of the gas are so far apart that they do not interact (except during collisions that are effectively elastic). A gas behaves more like an ideal gas at High Temperature and Low Pressure.

The Ideal Gas Law The constant term R/NA is referred to as Boltzmann's constant, in honor of the Austrian physicist Ludwig Boltzmann (1844–1906), and is represented by the symbol k: PV = NkT

To Be Continued…