Download Chapter7_1 - Department of Chemistry [FSU]

!Hcomb of benzoic acid (C6H5CO2H) is -3227 kJ/mol. When
a 2.442-g sample of benzoic acid is burned in a
calorimeter, all of the resulting heat is transfered to 2.5 kg
of water (c=4.184 J/g.K). What is the temperature change?
Calculate !Hrxn for
2 NOCl
N2 + O2 + Cl2
given the following set of reactions
N2 + O2
2NO + Cl2
2NO
2NOCl
!H = 180.6 kJ
!H = -77.2 kJ
Combustion of octane C8H18 produces carbon dioxide and water.
C8H18 + O2
CO2 + H2O
(a) Balance this reaction and calculate !Hocomb for 1 mol of octane, assuming water
forms as a gas;
!Hof = -208.45 kJ/mol for octane
!Hof = -393.5 kJ/mol for carbon dioxide
!Hof = -241.8 kJ/mol for H2O (g)
(b) How many liters of CO2 (at 25 oC and 1 atm, R = 0.0821 atm.L/mol.K) are formed
when 1 kg of octane is burned? How much work is done by the expanding CO2 as 1
kg of octane is burned (again, at 25 oC and 1 atm). (Hint, 1 J = 9.87.10-3 atm.L).
What is !E for the reaction? (Hint, the definition of H = E + PV, assume PV is done
by carbon dioxide only (ignore water and octane))
Atomic Structure: Quantum Theory
nuclear model from
Ratherford’s experiments
Problem with Classic Structure
accelerating charged
particle loses energy
The Nature of Light
! frequency (")
! amplitude
#= c
"
Electromagnetic Spectrum
Diffraction and Interference
diffraction
interference
here, light behaves as a wave
Blackbody Radiation
However:
0K
1000 K
1500 K
Max Planck, 1900
E = nh"
n is a positive whole number, quantum number
h is a constant
" is the frequency of light emitted
Photoelectric Effect
• threshold frequency
• no time lag
Einstein, ~1905
Ephoton = h"
> 2000 K
Photoelectric Effect
7.96. Electric power is typically stated in units of watts (1W
= 1J/s). About 95% of the power output of an incandescent
bulb is converted to heat and 5% to light. If 10% of that light
shines on your chemistry text, how many photons per
second shine on the book from a 75-W bulb? (assume a
wavelenght of 550 nm)
The Nature of Light
• electromagnetic radiation travels in waves
• at the speed of light (in vacuum, c = "#)
• intensity is either amplitude or number of photons/second
• energy of light is quantized, E = h"
• the energy of atom is also quantized, E = nh"
h = 6.626$10-34 J•s
Atomic Spectra
H
He
Na
sunlight
Ba
K
Atomic Spectra (Neon)
Atomic Spectra (H)
Rydberg equation
1 =R
!
1
22
_
1
n2
The Bohr Model of the
Hydrogen Atom
Niels Bohr proposed these postulates:
1. The H atom has fixed energy levels: stationary states
2. The atom does not radiate energy while in one of
those states
3. Change to another state: !E = !Ephoton = h"
The Bohr Model of the
Hydrogen Atom
Niels Bohr proposed these postulates:
E = h!
ground state: the
lowest energy
The Bohr Model of the
Hydrogen Atom
E = h!
the charge of the nucleus
-18
E = -2.18x10 J
Z2
n2
energy levels for the H atom
De Broglie: electrons are
waves
matter is wavelike:
#=
h
mv
electrons within atoms behave like waves
The Quantum-Mechanical
Model
Schrodinger equation:
d2%
d2%
d2%
8&2me
[E - V(x,y,z)]%(x,y,z)=0
+
+
+
dx2
dy2
dz2
h2
or
H% = E%
%2 is the probability that the electron is in a certain
region of space
The Quantum-Mechanical
Model
Schrodinger equation:
H% = E%
solutions (energy states) are associated with a given %,
called an atomic orbital
Hydrogen Atom
“point” probability
radial probability
Hydrogen Atom
32%
74%
99%
Atomic Orbitals
different energy states are associated with atomic orbitals
atomic orbitals are characterized by 4 (3) quantum numbers
n (1,2,3, etc.) is the size (level)
principal quantum number
l (from 0 to n-1) is the shape (sublevel)
angular momentum quantum number
ml (from -l to +l) is the orientation
magnetic quantum numbber
Atomic Orbitals
Sample Problem 7.5
Specify possible orbitals (sets of n, l, m) for n=3.
Atomic Orbitals
n (level)
1,2,3, etc
l (sublevel, shape)
s (l=0), p (l=1), d (l=3), f(l=4), etc
S orbital - m equals 0
Atomic Orbitals (s)
1 s orbital
3 s orbital