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Chemistry 121S
Worksheet 2 Notes
Summer 2006
J/gּ˚C
4.186
2.549
2.093
2.009
1.75
1.674
Substance
Water
Methyl Alcohol
Ice
Steam
Benzene
Wood (typical)
Substance
Soil (typical)
Air
Aluminum
Mercury
Gold
Lead
Oregon State University
Dr. Richard Nafshun
J/gּ˚C
1.046
1.046
0.9
0.138
0.13
0.128
(14) 1. A student obtains 5400 grams of water (approximately 6 quarts) at 23.0 ˚C.
Calculate the heat required to increase the temperature of the water to 100.0 ˚C.
heat = mcΔT = (5400 g)(4.18 J/gּ˚C)(100.0 ˚C – 23.0 ˚C) = 1738044 J or 1738 kJ
(Tfinal – Tinitial)
Note the positive energy (+1738 kJ) denotes the process is endothermic (energy
was taken in to heat the water.)
2.
A student obtains 5400 grams of water at 100.0 ˚C. Calculate the heat released
when temperature of the water decreases to 23.0 ˚C.
heat = mcΔT = (5400 g)(4.18 J/gּ˚C)(23.0 ˚C – 100.0 ˚C) = -1738 kJ
(Tfinal – Tinitial)
Note the negative energy (-1738 kJ) denotes the process is exothermic (energy
was given off by the system.)
If a 10,000 gram sample of gold absorbed all of this heat released from the water,
what would be the change in temperature of the gold sample?
The water gave off energy and the gold took in the energy.
heat = 1738044 J = (10,000 g)(0.13 J/gּ˚C)(ΔT)
ΔT = 1337 ˚C
3.
Steam comes in contact with your arm. What is the sensation? Why?
Hot! The process is releasing energy when the steam condenses to water. This is
an exothermic process and you are the recipient of the heat.
H2O (g) → H2O (l)
ΔH = (-)
(17) 3. Which of the following sets of quantum numbers is INCORRECT? Explain.
Sketch and label the orbital associated with each correct set of quantum numbers.
(A)
n = 1, l = 0, ml = 0, ms = +½.
(B)
n = 1, l = 1, ml = 0, ms = +½.
When n=1, l cannot be 0, it must be 0!
l is the sublevel quantum number (l = 0, 1, 2..., ∞) but as discussed in lecture, is limited
by n (it has a maximum of n-1; so, it can be stated that although l = 0, 1, 2..., ∞; l = 0, 1,
..., n-1)
l designates the shape of the electron cloud (orbital) (the region of space that represents
the volume that the electron occupies 90% of the time).
(C)
(D)
(E)
4.
n = 2, l = 0, ml = 0, ms = +½.
n = 2, l = 1, ml = 0, ms = +½.
n = 2, l = 1, ml = -1, ms = -½.
What is the difference between a 2s and a 3s orbital?
Size. Consider the 2s orbital, n = 2. Consider the 3s orbital, n = 3. n tells us
something about the energy (En=-RH/n2 in hydrogen) and the radii (rn=n2a0 in
hydrogen). As n increases, the size increases.
1s
2s
2p
(N) 1. Sketch the 1s, 2s, 3s, 2px, 2py, 2pz, and the five 3d orbitals. Label all axes.
These are presented on the July 8 handout and in the text on pages 304 and 306.
2.
A laser produces light having a wavelength of 610 nm. What is the energy
contained in one photon?
ν = c/λ = (3.00 x 108 m/s)/(610 x 10-9 m) = 4.92 x1014 1/s or Hz
E = hν = (6.626 x 10-34 J·s)(4.92 x1014 1/s) = 3.26 x 10-19 J (per photon)
3.
The de Broglie wavelength of a particle of mass 6.86 x 10-27 kg is 5.03 x 10-15 m.
How fast is the particle traveling?
λ = h/mv
(5.03 x 10-15 m) = (6.626 x 10-34 J·s)/[(6.86 x 10-27 kg)(v)
v = 1.92 X 107 m/s
4.
Discuss enthalpy, work, state, and non-state functions.
Enthalpy is a state function—independent of path. Work is not.
5.
Discuss line and continuous spectra.
Atoms produce line spectra—electron transitions from high energy levels to low
energy levels.
6.
Discuss the four quantum numbers (names, meanings, allowed values).
n, the principal quantum number. This is also known as the radial quantum number,
and defines the distance of the electron from the nucleus in the Bohr model. n also
describes the azimuthal angular momentum. n takes on integral values 1, 2, 3, ... .
l, the azimuthal quantum number. In Sommerfeld's generalization of the Bohr model,
the circular orbits of the electrons are replaced by elliptical orbits, and l describes
the shape of the orbit. l takes on the integral values 0, 1, 2, ... , n-2, n-1. If n=1,
l=0. l is sometimes called the reduced azimuthal quantum number, because the
Sommerfeld formulation used a quantum number k, which equals l+1. k=0
corresponds to no angular momentum, or a radial orbit which takes the electron
through the nucleus. This is unphysical, and is forbidden.
m, the magnetic quantum number. m takes on the integral values -l , -(l-1), ..., -1, 0,
1, ..., (l-1), l. In Sommerfeld's formulation, m described the orientation of the
ellipse. This is known as the magnetic quantum number because its effects are
generally observed only under the influence of strong magnetic fields (which set a
preferred spatial orientation).
s, the spin quantum number. This describes the spin of the electron, and is either +1/2
or -1/2.