1. 3
(C(s) + O2(g) à CO2(g) ΔH = -393.5 kJ) =
-1180.5kJ
2 (2H2(g) + O2(g)
à2H2O(l) ΔH = -571.7.kJ)=
-1143.4kJ
3 CO2(g) + 4
H2O àC3H8(g) + 5
O2(g)
= +2220 kJ
Sum 3C + 4 H2 à C2H8
ΔHrxn = -103 kJ
Note that for this rxn
ΔHrxn is also
ΔHformation
2. Given the
following standard enthalpies of formation,
Substance ΔHf
kJ/mol
NO2(g) +33.2
NH3(g) -46.1
H2O(l)
-285.8
Calculate the standard enthalpy
change, ΔHo, for the following
reaction:
2 NH3(g) + 7/2 O2(g) -à 2NO2(g) +
3H2O(l)
ΔHrxn = (sum
ΔHf products – sum
ΔHf reactants)
= [3(-285kJ) + 2(+33.2 kJ)] – [2(-46.1kJ +
0]
= -696.5 kJ
Answer ΔHrxn =
(6 Pts.)
3. Given the
following thermochemical equation describing the
combustion of butane
C4H10(g) (1 mol C4H10 =
58.0g).
2C4H10(g) + 13O2(g) -->8CO2(g) +
10H2O(g),
ΔHrxn = -5285 kJ
How many grams of butane must be burned in order to produce
41800kJ?
Answer: The equation above is for two mols of
butane or 2 (58) g = 116 g of butane when burned produces –5285 kJ of
energy. Your want to produce 41899
kJ so we divide the heat desiredby theheat produced from burning 116g of butane
-41600kJ/) -5285 kJ) x
116g = 917 g of butane must be
burned
4.
Calculate the frequency for a wave of electromagnetic
radiation
having a wavelength of 486
nanometers. (Given C = 3.00 x
108 m/s,
h = 6.626 x 10-34 J.s ΔE per photon = hν or ΔE=
hc/λ
answer: the equation which relates frequeny and
wavelength is c = λν
ν = c/ λ = 3.0 x 108 m/s / 486 x
10-9m =
6.17 x 1014s-1
5. A 200g
sample of water at 25.OoC absorbs 18000 J of thermal energy. What
will be its final temperature?
(Given 1 mol H2O = 180g and S.H. = 4.18 J )
(g C)
Answer 18000 J = (T final- 25)(180 g)(4.184
J/gC)
23.9 = T final- 25
48.9 = T final
6.
Calculate the energy, ΔE, of a photon of light having a frequency, ν, of
7.50 x 1014s-1 meters.
(Given C = 3.00 x 108 m/s,
h = 6.626 x 10-34 J s
Photon
Answer: We have to use the equation which
relates energy and frequency
ΔE = hν = (6.6 x
10-34Js)(7.50 x
1014s-1)
= 4.9 x 10-19J
Mulitple choice questions
circle the correct response1 thru 20. (3 pts.
each)
1.
Rutherford's conclusion that an atom has a tiny atomic nucleus relative
to the size of the atom and that most of an atom consists of empty space was
based on which observation below?
a. Measurement
of charge to mass ratio of electrons with a cathode ray
tube.
b.
Electrically charged oil drops fall slower when placed between
electrically charged metal plates.
c. Cathode
rays can be bent by electric and magnetic fields.
d. Most high
speed alpha particles passed through thin metal foils without being
deflected.
e. Atoms of
the same element may differ in the number of neutrons in the
nucleus.
Ans d
2. The experimental
evidence that electrons bound to atoms can only exist in certain discrete energy
levels comes from
a. experiments with mass
spectrometers
b. observation
that only certain wavelengths of light are emitted or absorbed by
atoms
c. Millikan's oil drop
experiment
d. Cathode ray tube experiments
done by J. J. Thomson
e. the Heisenberg uncertainty
principle
ans
b
3. Which of the
following sets of quantum numbers in not
permissible?
a. n = 2, = 0, ml = 0, ms =
+1/2
b. n = 2, = 1, ml = 2, ms =
-1/2
c. n = 3, = 2, ml = -2, ms =
-1/2
d. n = 3, = 2, ml = 0, ms =
+1/2
e.
n=1,l=0m1=0,ms=+1/2
ans---b-cannot-be-bigger-than-l
4. Louis de
Broglie made an important contribution to the development of Quantum Mechanics
Theory of the atom when he postulated that:
a. an electron can exist in an
atom only in certain discrete fixed energy levels.
b. no electron can have
identical values for all four quantum numbers
c. elements
show periodic repetition of properties.
d. that particles of matter show
characteristics of waves.
e. E =
hv
ans
d
5. The volume in
space around the nucleus of an atom where an electron with a particular energy
is likely to be found is called
a. a
node
b. an
orbital
c. a
photon
d. a wave
function
e.
quantized
ans
b
6. According
to the Heisenberg uncertainty principle, it is impossible to simultaneously
measure with great accuracy an electron's
a. position and
velocity
b. velocity and
energy
c. wavelength and
frequency
d. frequency and
energy
e. none is
correct
ans
a
7. The quantity of
thermal energy gained or lost when a physical or chemical change takes at
constant pressure is called the
a. entropy
change
b. heat
capacity
c. thermochemical
equation
d. enthalpy change
e. temperature
change
ans
d
8. Physical or
chemical changes in which thermal energy is lost from the system to the
surroundings are said to be
a.
exothermic
b.
endothermic
c.
rapid
d.
nonspontaneous
e. none is
correct
ans
a
9. Putting
electrons into orbitals beginning with the lowest
energy
orbital closest to the nucleus is required
by
a. Pauli’s principle.
b. the aufbau
principle.
c. Hund’s
rule.
d. effective nuclear
charge.
e. None is
correct.
Ans
b
10. The principal quantum
number, n,
a. tells the size of an orbital
and largely determines it energy
b. tells the shape of an
orbital
c. describes the position in
space of an orbital
d. limits the
number of electrons in an orbital to two
e. none is
correct
ans
a
11. The enthalpy
change, ΔH, which accompanies a
physical or chemical change which takes place in a single step when compared
with the ΔH for the same overall change taking place in several steps
is
a. always
smaller
b. always
larger
c. always the
same
d. sometimes
larger, sometimes lower depending on the entropy
change
e.
impossible
to predict based on the information provided
f.
ans c (Hess’s
Law)
12. Given the following
thermochemical equation
HI(g) 1/2 H2(g) + 1/2
I2(s) ΔH =
-25.9kJ
Find the ΔHrxn for the
reaction
H2(g) +
I2(s)
2HI(g)
a. ΔH = +25.9
kJ
b. ΔH = -25.9
kJ
c. ΔH = -12.45
kJ
d. ΔH = +51.8
kJ
e. none is
correct
ans d ( reverse equation and
multiply by 2 change sign when reversing equation)
13. Which of the following
substances has a standard enthalpy of formation equal to
zero?
a.
CO2(g)
b.
O2(g)
c.
NO(g)
d.
O2-
e. none is
correct
ans
b
14. Properties
that depend only on the initial and final states of the system and not on how
the system gets from the initial to the final state are
called
a. enthalpy
properties
b. state
functions
c. standard state
properties
d. conservation
functions
e. none is
correct
ans
b
15.
Constructive interference of light waves occurs when light
waves
a. interact
such that their amplitudes add together producing a wave having greater
amplitude
b. interact
such that their amplitudes cancel
c. are absorbed by electrons
bound to atoms
d. have
nodes
e. none of the above answers is
correct.
Ans
a
16. The significance of Max
Planck's work was that he was the first to
a. observe the photoelectric
effect
b. observe the discontinuous
line spectrum of hydrogen
c. propose the
principle of conservation of energy
d. propose that energy is
ultimately transmitted by little particles (or packets) called quanta (or
photons)
ans
d
17. The number of p
orbitals in the 3 p subshell is:
a.
1
b.
3
c.
5
d.
7
e. none is
correct
ans
b
18. Which of the following
drawings depict the shape of a Px
orbital
a.
c.
this was suppsed to be an S
orbital
This was supposed to be a d orbital
b.
d.
This was to be a
Py
this was supposed to be a px
e. none is
correct
19. The standard heat of
formation of NO2(g)is ΔHf = +33.2 kJ/mole. This means
that
a. One mole of
NO2(g) contains a total of 33.2 kJ of energy
(in
absolute terms) at standard
conditions.
b. One mole of
NO2(g) contains 33.2 kJ more energy than the
elements
from which it was formed at
standard conditions.
c. One mole of
NO2(g) contains 33.2 kJ less energy than the
elements
from which it was formed at
standard conditions.
d. One mole of
NO2(g) is unstable and will break down
spontaneously
into its elements at standard
conditions.
e. The entropy of one mole of
NO2 will be zero at standard
conditions.
Ans
b
20. The Pauli exclusion
principle states that
a. no two electrons in a given
atom can have exactly the same
set of four quantum
numbers
b. only certain electrons can
penetrate to the nucleus of an
atom
c. that d and f orbitals are
excluded from the n=2 shell
d. it is impossible to know
exactly both the position and the
velocity of an
electron
e. diffraction patterns are
excluded when electrons are emitted
by
atoms.
Ams
a