Key - Grossmont College

shootceaselessUrban and Civil

Nov 16, 2013 (3 years and 8 months ago)

67 views

Grossmont College Chemistry 141 Exam 2 Fall 2013

Name: __________
_________________________Date
: ________

Instructor: Diana Vance



Exam 2

Part 1: Multiple Choice (2 points each)

Directions: Please circle the
best

answer for each of the following questions.

1.

Assuming ideal behavior, which of these gas samples will have the greatest volume at STP?


a.

1 g of H
2

b.

1 g of Ar

c.

1 g of O
2

d.

all of the above

e.

not enough information


2.

Which of the following is true of the internal energy of a system and its surroundings durin
g an energy
exchange with a negative

E
sys
?


a.

The internal energy of both the system and the surroundings increases.

b.

The internal energy of the system increases and the internal energy of the surroundings decreases.

c.

The internal energy of both the system a
nd the surroundings decreases.

d.

The internal energy of the system decreases and the internal energy of the surroundings increases.

e.

none of the above


3.

What is a photon?


a.

A packet of light.

b.

A packet of force.

c.

The smallest particle.

d.

The way of any
interaction.

e.

Charge transporting particle.


4.

Using the graph below, determine the gas that has the lowest density at STP.



a.

A

b.

B

c.

C


d.

D

e.

All of the gases have the same density at STP.

Grossmont College Chemistry 141 Exam 2 Fall 2013

Instructor: Diana Vance


Page
2

of
6


5.

Which statement is true about kinetic molecular theory?

a.

A single
particle does not move in a straight line.

b.

The size of the particle is large compared to the volume.

c.

The collisions of particles with one another is completely elastic.

d.

The average kinetic energy of a particle is not proportional to the temperature.

e.

none

of the above


6.

A sun burn is caused by overexpose to ______________ radiation.

a.

ultraviolet

b.

gamma

c.

microwave

d.

x
-
ray

e.

radio


7.

What value of the angular momentum quantum number, l, is represented by a d orbital?


a.

0

b.

1

c.

2

d.

3

e.

4


8.

Which statement is false?


a.

An exothermic reaction gives off heat to the
surroundings
.

b.

Enthalpy is the sum of a system’s internal energy and the product
of pressure and volume.

c.


H
rxn
is the heat of reaction.

d.

Endothermic has a positive

H.

e.


E
rxn

is a measure of heat
.


9.

Two aqueous solutions are both at room temperature and are then mixed in a coffee cup calorimeter. The
reaction causes the temperature of the resulting solution to fall below room temperature. Which of the following
statements is true?

a.

The products have a lower potential energy than the reactants.

b.

This type of experiment will provide data to calculate

E
rxn
.

c.

The reaction is exothermic.

d.

Energy is leaving the system during the reaction.

e.

none of the above; all statements are true.


10.

Whic
h
rule
(
s
)

about lab safety is true?

a.

If a small piece of matter is lodged in the tip of a pipet, buret, or eye dropper, it is acceptable to blow the
piece out with your mouth.


b.

If a chemical smells good, it must taste good and therefore it can be eaten.


c.

Eye protect is needed while you are reading or writing in the lab if other students are still performing their
experiments.

d.

If a glass drops and shatters, you should immediately pick up all large pieces with unprotected hands.

e.

You should deeply

inhale all chemicals at the opening of the reagent bottle to smell it.



Grossmont College Chemistry 141 Exam 2 Fall 2013

Instructor: Diana Vance


Page
3

of
6


Part 2: Short Answer

Directions: Answer each of the following questions. Be sure to use complete sentences where appropriate. For
full credit be sure to show all of your work.


1.

In constructing a barometer, what advantage is there in choosing a dense liquid (3 points)?


A more dense liquid has a shorter column of liquid in a barometer and therefore we do not
need to have a very tall barometer to measure atmospheric pressure.


2.

Determine the total volume of all gases (at STP) formed when 50.0 mL of TNT, C
3
H
5
(NO
3
)
3
,
density = 1.60 g/mL and molar mass = 227.10 g/mol, react according to the following
reaction

(10 points)
:

4 C
3
H
5
(NO
3
)
3 (l)



6 N
2 (g)

+ O
2 (g)

+ 12 CO
2 (g)

+ 10 H
2
O

(g)

















































































































































































































































Or




































(
















)



























3.

What
is the volume of 9.783 x
10
23

atoms of kypton at 9.25 atm and 239 °C (6 points)?












(








)
(










)
(



)






























Grossmont College Chemistry 141 Exam 2 Fall 2013

Instructor: Diana Vance


Page
4

of
6


4.

A gas bottle contains 0.250 mol of gas at 730 mm Hg pressure. If the final pressure is 1.15
atm, how many moles of gas were added
to the bottle

(6 points)
?




























(






)
(



















)





































5.

Why are the various forms of radiant energy
called electromagnetic radiation

(3 points)
?

All these forms of light have perpendicular, oscillating electric and magnetic fields that travel
together through space.

6.

How does the concept of an orbit in the Bohr model of the hydrogen atom differ from the
concept of an orbital in quantum theory

(4 points)
?

The Bohr model orbit showed the quantized nature of the
electron

in the atom as a
particle

moving

around the nucleus in concentric orbits, much like
planets moving around the sun.

In quantum theory, an o
rbital is a region of space where the probability of finding the
electron is high. The electron is not viewed as a particle, but as a wave, and it is not confined
to a clearly defined orbit; rather, we refer to the probability of the electron being at vari
ous
locations around the nucleus.

7.

How is Hess’ Law consistent with the law of conservation of energy (3 points)?


When we apply Hess’ law all the heat is accounted for in the reaction; energy is neither
created nor destroyed when using Hess’ law.


8.

The mi
neral magnetite (Fe
3
O
4
) is magnetic, whereas iron(II) oxide is not (5 points).

a.

Write and balance the chemical equation for the formation of magnetite from iron(II)
oxide and oxygen gas.


6 FeO

(s)

+ O
2 (g)



2 Fe
3
O
4 (s)


b.

Given that 318 kJ of heat are rel
eased for each mole of Fe
3
O
4

formed, what is the
enthalpy change of the balanced reaction of formation of Fe
3
O
4
from iron(II) oxide and
oxygen gas?




































Grossmont College Chemistry 141 Exam 2 Fall 2013

Instructor: Diana Vance


Page
5

of
6



9.

A system releases 673 kJ of heat and does 115 kJ of work on the surroundings. What is the
change in internal energy of the system (3 points)?













(




)









10.

A laser pulse has a wavelength of 505 nm (10 points).

a.

What is the freq
uency of the laser pulse?































b.

What is the energy of the photon?










(











)
(








)
(







)













c.

It contains 4.40 mJ of energy. How many photons are in the lase
r pulse?

















































11.

What is the photoelectric effect (2 points)?

Many metals emit electrons when light of high enough energy is shone on them. (Thi
s
observation brought the classical view of light into question.

12.

Use the information provided to determine

H
°
rxn

for the
following reaction

(5 points)
:

CH
4 (g)

+ 3 Cl
2 (g)



CHCl
3 (g)

+ 3 HCl

(g)




H
°
rxn

= ?



























(



















)

(





















)






(
(



)
(




)

(




)
(




)

)

(
(



)
(




)

(



)
(



)
)











Substance


e
°
f

(kJ/mol)

CH
4 (g)

-
75

CHCl
3 (g
)

-
134

Cl
2 (g)

0

HCl

(g)

-
92

Grossmont College Chemistry 141 Exam 2 Fall 2013

Instructor: Diana Vance


Page
6

of
6



13.

Calculate the amount of heat (in kJ) required to raise the temperature of a 79.0 g sample of
ethanol from 298.0 K to 385.0 K. The specific heat capacity of ethanol is 2.42 J/g °C

(5
po
ints)
.













(





)
(







)
(











)
(






)







(





)
(







)
(





)
(






)
(






)







14.

Calculate the standard enthalpy of formation of solid magnesium hydroxide using the
following data

(8 points)
:

2 Mg

(s)

+ O
2 (g)



2 MgO

(s)



H
°

=
-
1203.7 kJ

MgO

(s)

+ H
2
O

(l)



Mg(OH)
2 (s)



H
°

=
-
36.7 kJ

2 H
2
O

(l)



2 H
2 (g)

+ O
2 (g)



H
°

= +571.6 kJ


Equation for the formation of Mg(OH)
2
from the elements:

Mg

(s)

+ O
2 (g)

+ H
2 (g)



Mg(OH)
2 (s)


H
f
°

= ?


(
2 Mg

(s)

+ O
2 (g)



2 MgO

(s)



H
°

=
-
1203.7 kJ
) x ½

(
2 H
2 (g)

+ O
2 (g)



2 H
2
O

(l)




H
°

=
-
571.6 kJ
) x ½

+

MgO

(s)

+ H
2
O

(l)



Mg(OH)
2 (s)



H
°

=
-
36.7 kJ

Mg

(s)

+ ½ O
2 (g)

+ H
2 (g)

+ ½ O
2 (g)

+ MgO

(s)

+ H
2
O

(l)



MgO

(s)

+ H
2
O

(l)

+ Mg(OH)
2 (s)


Mg

(s)

+ O
2
(g)

+ H
2 (g)



Mg(OH)
2 (s)







(






)
(


)

(






)
(


)

(






)









15.

Why don’t we observe the wavelength of everyday macroscopic objects (3 points)?


Due to the large mass of macroscopic objects, the deBroglie wavelength is extremely sm
all.
The wavelength is so small that it is impossible to detect compared to the size of the object.


16.

An electron in the n = 7 level of the hydrogen atom relaxes to a lower energy level, emitting
light of 1005 nm. What is the value of n for the level to wh
ich the electron relaxed? R
H

=
1.097 x 10
-
2
nm
-
1

(4 points).






(









)






(









)
(








)