Unit 1: Stoichiometry and Gases

By Alex and Maria

Tour of the Periodic Table

– Groups and Periods

• Groups: vertical columns of elements with similar chemical and physical properties

• Periods: Horizontal columns

Element Groups

• Groups 1A: Alkali Metals• Group 2A: Alkali Earth

Metals• Group 3A-4A: unnamed• Group 5A: Pnictogens• Group 6A: Chalcogens• Group 7A: Halogens (salt)• Group 8A: Noble Gases

Naming Ionic Compounds

-Ide -Ite -Ate Per…Ate Hypo-Monatomic NO2

- NO3-

Exceptions ClO2- ClO3

- ClO4- ClO-

OH- SO3- SO4

2-

CN-

•An ionic compound is a metal cation bonding to a non-metal anion•Binary compounds are two nonmetal compounds, like NF3 (add prefix)

Protons, Neutrons, Electrons and Isotopes

• An Isotope is an atom with the same atomic number but different mass numbers because of a difference in the number of neutrons.

• The atomic number of an element is the number of protons

• Neutrons and Protons add up to the mass number of an ion/element

• The number of electrons is determined by the charge of the ion

Example

Element Atomic

#

Mass # # of

Protons

# of Neutrons

# of Electrons

Na 11 23

Na+ 11 23

Na 11 24

11

12

13

1112

11

1011

11

Percent Abundance

• Percent Abundance is the percentage of atoms of each isotope in a sample

• % abundance= • (# of atoms of given isotope) x 100%

(total # of atoms of all isotopes of that element)

Mass Mole Relationships/Percent Composition

• Mass to Mole Relationships:

Mass of A Moles of A Moles of B Mass of B

•Percent Composition=

•(MA/MT) x 100%

Empirical and Molecular Formula

• Empirical Formula: (HINT-Assume 100g sample)

= % composition ÷ (Smallest number of moles)

molar mass

• Molecular Formula:

(Mexp/Memp) x (Elements in Compound)

Example (Empirical Formula)• You have a compound composed of 49.8% C, 5.15% H,

16.49% O, and 28.87% N. Find the empirical formula• 49.48g C x 1 mol C = 4.120mol C = 4 mol C

12.011g C 1.031

• 5.15g H x 1 mol H = 5.110 mol H = 5 mol H 1.0079g H 1.031

• 16.49g O x 1 mol O = 1.031 mol O = 1 mol O 15.9994g O 1.031

• 28.87g N x 1 mol N = 2.061 mol N = 2 mol N 14.0067g N 1.031

C4H5ON2

Example (Molecular Formula)

• If the molar mass for the previous compound is 194.2 g/mol, what is its molecular formula?

• Theoretical molar mass = 4(12.011 g/mol C) + 5(1.0079 g/mol H) + (15.9994 g/mol O) + 2(14.0067 g/mol N)

= 97.0963 g/mol

• 194.2 g/mol ~ 2 96.0963 g/mol

• 2(C4H5ON2) = C8H10O2N4

Balancing Reaction Equations/ Stoichiometry

• To balance a reaction equation be sure to have the same number of elements on the reactant and products side.

• See mass to mole relationship for stoichiometry.

Limiting Reactants/ Percent Yield

• Using stoichiometry find which reactant produces less of either product. This reactant is the limiting reactant.

• (Mexp/Mtheor) x 100%

Hydrates

• Hydrates are compounds which molecules of water are associated with the ions of the compound.

• There is no simple way to predict how much water will be present in a hydrate compound; it must be determined experimentally.

• Mass of Water=Mass of Hydrate Compound – Mass of anhydrous compound

Partial Pressure

• Partial pressure: PA=χAPTotal

Ptotal=((nA+nb+nc…)RT)/V

χA= na/ntotal

• Mole fraction: Ratio of the number of moles of one substance to the total number of moles in a mixture of substances

Ideal Gas Law PV = nRT

P = Pressure (atm) 1atm = 760torr = 760mmHg

V = Volume (L)N = # of molesR = Rate

= .08206 (L∙atm/mol∙K)

T = Temperature (K) K =°C + 273K

m/v = (PM)/(RT) = ρ

GAS….

Kinetic Molecular Theory

• Tiny particles surrounded by much empty space

• Constantly moving• Energy (speed2)

proportional to temperature (T) in Kelvin

• Particles collide without losing energy (preferably an elastic collision)

R.M.S speed/Effusion/Diffusion

• √(3RT)/M = √u2 R= 8.314 J/mol∙K (J=kg∙m2/sec2)T = Temperature (K)M = Molar Mass (kg/mol)

• Effusion is going from a container into a vacuum

• Diffusion is the mixing of two gases• rate1/rate2= √M2/M1

Non-Ideal Gas Law (Van der Waals)

• (Preal+a(n/v)2)(Vreal-bn)=nRT• a= Attractive forces (atm∙L2/mol2)• b= Molecular volume (L/mol)• a(n/v)2 is the correction for intermolecular forces• bn is the correction for molecular volume• a and b are Van der Waals constants

GAS!