Chem 10 – Exam 3
Useful information: R = 0.08206 liter atm/ mol K = 8.3145 J/mol K
h = 6.626 x 10
34
J s, N
A
= 6.02 x 10
23
, mass of an electron = 9.11 x 10
31
kg, mass of a proton =
1.673 x 10
27
kg,
1 atm = 101325 Pa = 760 torr, F=95485 coul/mol, E = h
ν
= hc/
λ
, c=3 x 10
8
m/s, E
n
= (n+1/2)h
ν
,
ν
= (1/2
π
) (k/
μ
)
1/2
,
μ
= m
1
m
2
/(m
1
+m
2
)
E
J
= h
2
/(8
π
2
I) J(J+1), I=
μ
R
2
,
E
n
= n
2
h
2
/8mL
2
1.
What is the energy (in kJ) of a mole of 500 nm photons?
E = hc/
λ
= 3.98 x 10
19
J/photon = 2.39 x 10
5
J/mol =
239 kJ/mol
2.
The infrared spectrum of CO has a peak at 2145 cm
1
. What is the force constant of the CO
bond? (Carbon has a mass of 12 amu and oxygen has a mass of 16 amu.)
μ
= 12 x 16/(12 + 16) = 6.86 amu = 1.14 x 10
26
kg
1/
λ
= 2145 cm
1
= 2.145 x 10
5
m
1
E = hc(1/
λ
) = h(2
π
)
1
(k/
μ
)
1/2
,
solve for k.
k = (2
π
c 1/
λ
)
2
μ
= 1864 N/m
3.
Consider an electron in a 0.70 nm onedimensional box. What wavelength of photon is
needed to excite it from the n = 2 to the n = 3 level.
Δ
E = (3
2
– 2
2
) h
2
/8mL
2
= 6.15 x 10
19
J = hc/
λ
λ
= 3.23 x 10
7
m
= 323 nm
4.
The infrared absorption for
14
N
16
O is at 1876 cm
1
. Determine the wavenumber of the
infrared absorption of the
14
N
18
O molecule. (N has a mass of 14 amu. Take
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 Spring '10
 G
 Chemistry, Electron, Proton, Mole, Rate equation, initial concentration

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