1. N2(g) + 3H2(g) -> 2NH3(g) ΔHorxn= -92.6 kJ/mol.
Quiz 4
Consider the following reaction
N2(g) + 3H2(g) -> 2NH3(g) ΔHorxn= kJ/mol.
If 2.0 moles of N2 react with 6 moles of H2 to form NH3, calculate the work done (in joules) against a pressure of 1.0 atm and 25 oC. What is ΔE for this reaction? (Assume the reaction goes to completion.)
w= 9.9 kJ
ΔE= kJ
2/23/2019
S.A. McFarland©2006

2. 2CH3OH(l) + 3O2(g) -> 2CO2(g) + 4H2O(l) ΔHorxn= -1452.8 kJ/mol.
Quiz 4
Methanol is an organic solvent and is also used as fuel in some automobile engines. From the following data, calculate the standard enthalpy of formation of methanol:
2CH3OH(l) + 3O2(g) -> 2CO2(g) + 4H2O(l) ΔHorxn= kJ/mol.
ΔHf(CH3OH)= kJ/mol
2/23/2019
S.A. McFarland©2006

3. The Electronic Structure of Atoms
Ch. 7

4. n (principal quantum number) = 1,2,3,…
Some terminology
Ground state
Lowest energy electronic configuration
For H atom, electron is in n=1 orbit
Excited state
Higher energy configuration
For H atom, electron is in n>1 orbit
Absorption of photon
Requires energy input
Quantized
Electron moves to higher level
Emission of photon
Releases energy
Electron moves to lower level
En = -RH
( ) 1 n2
n (principal quantum number) = 1,2,3,…
RH (Rydberg constant) = 2.18 x 10-18J
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5. ( ) ( ) ( ) Ephoton = DE = Ef - Ei 1 Ef = -RH n2 1 Ei = -RH n2 1
nf = 1
ni = 3
nf = 2
ni = 3
Ef = -RH
( ) 1 n2 f
nf = 1
ni = 2
Ei = -RH
( ) 1 n2 i i f
DE = RH
( ) 1 n2
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6. ( ) DE = RH 1 n2 Ephoton = Ephoton = 2.18 x 10-18 J x (1/25 - 1/9)
Calculate the wavelength (in nm) of a photon emitted by a hydrogen atom when its electron drops from the n = 5 state to the n = 3 state. i f
DE = RH
( ) 1 n2
Ephoton =
Ephoton = 2.18 x J x (1/25 - 1/9)
Ephoton = DE = x J
Ephoton = h x c / l
l = h x c / Ephoton
l = 6.63 x (J•s) x 3.00 x 108 (m/s)/1.55 x 10-19J
l = 1280 nm
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S.A. McFarland©2006

7. Why is e- energy quantized?
Electrons in orbits behave like standing waves (De Broglie, 1924)
As a wave, the length of the wave must fit the circumference of the orbit exactly
Particle (mass) and wave (wavelength) properties are related
2pr = nl l = h/mu
u = velocity of e- (in m/s)
m = mass of e- (in kg)
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8. What is the de Broglie wavelength (in nm) associated with a 2
What is the de Broglie wavelength (in nm) associated with a 2.5 g Ping-Pong ball traveling at 15.6 m/s?
l = h/mu
h in J•s
m in kg
u in (m/s)
l = 6.63 x / (2.5 x 10-3 x 15.6)
l = 1.7 x m = 1.7 x nm
1 J = 1 kg m2 / s2
Wave-like properties of a large object like a tennis
ball cannot be detected…
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S.A. McFarland©2006