Class Notes (1,000,000)
US (430,000)
LSU (7,000)
CHEM (100)
Kolniak (30)
Lecture 6

CHEM 1201 Lecture Notes - Lecture 6: Sodium Azide, Chemical Formula, Molecular MassPremium


Department
Chemistry
Course Code
CHEM 1201
Professor
Kolniak
Lecture
6

This preview shows page 1. to view the full 5 pages of the document.
CHEM 1201 Lecture 6 - Patterns of Chemical Reactivity
First: Combination Reactions
Two or more reactants combine to form single product.
A + B → C
● Consider:
2Mg(s) + O2(g) → 2MgO(s)
Since there are fewer products than reactants, the Mg has combined with O2 to form
MgO.
Note that the structure of molecules has changed.
As reactants, Mg consists of closely packed atoms (solid) and O2 (gas) consists of
dispersed molecules.
As a product, MgO consists of a lattice of Mg2+ and O2 ions (solid). Remember common
ions
Second: Decomposition Reactions
A single reactant produces a mixture of products.
C → A + B
● Consider:
2NaN2(s) → 2Na(s) + 3N2(g)
The reaction which ocuurs in an air bag
Since there are more products than reactants., the sodium azide has decomposed into
Na and nitrogen gas.
Third: Combustion Reactions
These reactions generates heat and light (ex: flame)
Usually, combustion is the burning of an organic substance (hydrocarbon, CxHy) in the
presence of oxygen, O2.
The products of a combustion reaction are carbon dioxide, CO2, and water, H2O also a
little heat energy may be released.
The amounts of carbon dioxide, CO2, and water, H2O produced as products depend on
the quantity of carbon and hydrogen in the reactant hydrocarbon.
Example: Propane undergoing combustion.
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l) + heat (hv)
Heat is a form of energy described by a formula (hv)
Identify the following types of reactions:
C2H6(g) + 7O2(g) 4CO2(g) + 6H2O(l)
■ combustion
(NH4)2CO3(s) 2NH3(g) + H2O(l) + CO2(g)
■ decomposition
8Fe(s) + S8(s) 8FeS(s)
■ combination
2CuO(s) 2Cu(s) + O2(g)
■ decomposition
ATOMIC (Micro scale) and Molecular Weights (MACRO scale)
You're Reading a Preview

Unlock to view full version

Subscribers Only

Only page 1 are available for preview. Some parts have been intentionally blurred.

Subscribers Only
First: Microscale
The mass spectrometer (1933) is an instrument used to determine mass of small
particles / atoms in relation to the mass of a Carbon-12 isotope .
Carbon-12 isotope is the STANDARD for which the atomic masses for ALL the other
elements in the Periodic Table is determined
Why choose Carbon-12 isotope to develop the atomic masses for all the elements in the
periodic table? Stability C-12 is the most stable readily occurring isotope known in
existence.
Atomic mass units (amu) are used to define extremely small masses (Micro scale):
atoms, electrons, protons, neutrons, etc.
By DEFINITION: a single carbon -12 isotope/atom is 12 amu
Hence, the atomic mass for any element is DEFINED in relation to the mass of
carbon –12.
AND, the atomic mass of EVERY elemental isotope is defined in relation to the
carbon 12 isotope.
What do I mean by this? The mass spec (below) uses the C-12 isotope as a basis for
comparison to the unknown mass of some atom/isotope - generating a mass ratio that is
converted to amu’s.
● Example:
With the mass spectral data it can be established that the ratio of the mass of
16O to 12C is 1.3329. What is the mass of the 16O atom?
The ratio of masses is 16O/12C = 1.3329. The mass of 16O = 1.3329 times the
mass of 12C.
Mass of 16O = 1.3329 x 12 amu = 15.9948 amu
Average atomic mass:
Most elements occur in nature as a mixture of isotopes.
The atomic weight listed for an element in the periodic table is the WEIGHTED
AVERAGE of all the isotope's masses for that element that occur in nature.
The Mass Spec can also determine the percent abundance of various isotopes in a
mixture.
● Formula:
Av. Mass = w1% (mass1) + w2% (mass2) + … +
Note: the average atomic mass of an element is not the sum total of the masses of
protons, neutrons and electrons. The reason is related to Einstein’s famous E = mc2
equation. Some of the mass of the particles in the nucleus is converted to energy that
holds the atom together. So the mass of the atom is always less than the sum of the
masses of the subatomic particles.
● Example:
Naturally occurring carbon is composed of 98.892 percent 12C and 1.108
percent 13C. The masses of these nuclides are 12 amu (exactly) and 13.00335
amu, respectively. We calculate the average atomic mass of carbon as follows:
(0.98892)(12 amu) + (0.01108)(13.00335 amu) = 12.011 amu (The
average atomic weight of C on the periodic table)
You're Reading a Preview

Unlock to view full version

Subscribers Only