This document contains everything you need to do the Monday's CW
assignment at home. You need pages 73 (a table of all values of specific
heats needed), p 81 (you already got this as a handout before) and 82
from the Zumdahl textbook with questions. You also have the directions
that were given in class with helpful hints on solving many of the problems,
as well as the grading RUBRIC.
Page 1 (this page)
Page 2 - Zum p. 73 (specific heats)
Page 3 -Zum p. 81
Page 4 -Zum p.82
Page 5 - Directions
Page 6 - RUBRIC
This was an 8 point assignment with up to 4 pts ex cr possible.
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l
3.6
Energy and Energy Changes
73
i
iBecause water is such a fanriliar and
converrieni substance to use vuherr solvinq
,'..'
,specitic lteat problclt)s, stLtdet)ts someiimes
:believe that these calculations are fol water
i'-,'^^
only. Iable 3.2 qivcs the specific heat
lcapacities for a verriety of substances. lt!
,probably a good ic'lea to Ltse Il.tese for
lexamples in adclition to using water.
TABLE 3.2
The Specific Heat Capacities of Some Common Substances
Specific Heat Capacity (J/g'C)
Substance
water (0* (liquid)
4.184
water (s) (ice)
2.03
water (9) (steam)
2.0
aluminum
0.89
;
iron
(s)
0.45
mercury
carbon
silver
gold
(s)
(/)
0:14
(s)
0.71
(s)
0.24
(s)
0.13
*The symbols (s), (0, and (9) indicate the solid, liquid, and gaseous
states,
respectivelv.
There is another important factor: the identity of the substance,
Different substances respond differently to being heated. We have seen
that 4.184 J of energy raises the temperature of 1 g of water 1 oC, In contrast, this same amount of energy applied to 1 g of gold raises its temperature by approximately 32 "C! The point is that some substances require relatively large amounts of energy to change their temperatrlres, whereas others
reqlrire relatively little. Chemists describe this difference by saying that substances have different heat capacities. The antount of energy required to
change tlrc tentltercfitre of one grcmt of a sr,tbstance by one Celsius clegree is
cdlled its specific heat capacity or, more commonly, its specific heat. The
specific heat capacities for several substances are listed in Table 3.2, You can
see from the tabie that the specific heat capacity for water is very high com*
pared to those of the other sllbstances listed. This is why lakes and seas are
much slower to respond to cooling or heating than are the surrounding land
MASSCS.
EXAMPLE
3.6
to mal(e sLlrc' studonls know that
:here is ;r dif'ferent specific lreat capacity fc,r
lach of the tlrree physical states.
rt is r:sel'trl
Calculations lnvolving Specific Heat Capacity
a. What quantity of energy (in joules) is required to heat a piece of iron
weighing 1.3 g from 25 oC to 46'C?
b. What is the answer in calories?
ilnlu'i:ioli
a. It is helpful to draw the followi ng diagram to represent the problem.
.tT*--:
l.J^--.----_-l
s uon
I T=)\o(-""
t'
-\\
I
I
L_/
|
I
? joules
-
F€.*f"""r]
I r=a6ic
1'i,
I
81
Additional Problems
49. Convert the following numbers of joules (J) into kilojoules (kJ). (Remember: kilo means 1000.)
a. 243,000 J
c, 0,25I J
b. 4.184 J
d, 450.3 J
50. Perform the indicated conversions
a. 45.62 kcal into kilojoules
b. 12,94 kJ into kilocalories
c. 2.151 kJ into calories
d. 5,721kcal into joules
63, If solid iron pellets and sulfur powder are poured into a
container at room temperature, a simpie _
has
been made. If the iron and sulfur are heated until a chemical reaction takes place between them, a(n)
form.
of energy required (in calories) to
heat I45 g of water fuom 223 'C to 75.0 'C.
51, Calculate the amount
52.
Additional Problems
If 72.4 kJ of heat is applied to a 952-9 block of metal,
the temperature of the metal ihcreases by 10.7 'C. Calculate the specific heat capacity of the metal in J/g
65.
'/..
53. Calculate the energy reqrlh'ed (in joules) to heat 25.0 g
of gold from 120. 'C to 155 'C. (See Table 3,2.)
54. It takes L25 kJ of energy to heat a certain sample of pure
silver from l2-,0 "C to 75.2 oC. Calculate the mass of the
sample of siiver.
55,
If 50. J of heat is applied to
10. g of iron, by how much
(See Tab\e 3,2,)
will the temperature of the iron increase?
will
64. Pure substance X is melted, and the liquid is. placed in
an electrolysis appalatus such as that shown in Figure
3.3. When an electric curent is passed through the liquid, a brown solid folms in one chamber and a white
solid forms in the othel chamber. Is substance X a compound or an element?
oc.
:.
_
If
a piece of hard white blackboaril chalk is heated
strongly in a flame, the mass of the piece of chalk will
decrease, and eventualiy the chalk will crumble into a
fine white dust. Does this change suggest that the chalk
is composed of an element or a compound?
66. During a very cold winter, the temperature may remain
below freezing fol extended periods, However, fallen
snow can still disappear, even though it cannot melt. This
is possible because a solid can vaporize directly, without
passing through the liquid state. Is this'process (sublimation) a physical or a chernical change?
56. Calculate the quantity
of heat lequired to raise the temperatule of a 852.5-9 sample of iron from 40.1 oC to
75.5 'C.
57, The specific heat capacity of silver is 0,24 Jlg oC, Express
this in terms of calories per gram per Celsius degree,
58.
The specific heat capacity of gold is'0.13 J/g "C. Calculate the specific heat capacity of gold in callg 'C.
59. Three separate 75.0-9 samples of copper, silver, and
gold are available. Each of these samples is initially at
24.0 "C, and then 2.00 kJ of heat is applied to each
sample. Which sample will end up at the highest tem-
67. Perfolm the indicated conversions.
a, 4.52 cal to kilocalories
b, 5.27 kcal to joules
c. 852,000 cal to kilojoules
d. 352,4 kcal to kilojoules
e, 5.'72 kJ to calolies
f. 4.52 x 103 J to kilojoules
68, Calculate the amonnt of energy required (in joules) to
heat2.5 1cg of water from 18.5 'C to 55.0 'C.
69.
perature?
,#
60. If the temperatures of separate 25.0-9
samples of gold,
mercury, and carbon are to be raised by 20. oC, how much
heat (in joules) must be applied to each substance?
6I. A 22.5-9 sample of metal X requires 540. J of energy
to
heat it from 10. oC to 92 oC. CaTculate the soecific heat
capacity of metal X.
62. A 35.2 g sample of metal Z requires l25I J of energy to
heat the sample by 25.0 oC, Calculate the specific heat
capacitv of metaL Z.
if
10. J of heat is applied to 5.0-g samples of each of the
substances listed in Table 3.2, which substance's temperature will inclease the most? Which substance's temperature will increase the least?
70, A 5-g sample of aluminum and a 5-g sample of iron are'
heated in a boiling water bath in separate test tubes.
The test tubes are then placed together into a bealcer
containing ice. Which metal will lose the most heat in
cooling down?
71. Hydrogen gives off L20, Yg of energy when burned in
oxygen, and methane gives off 50. J/g under the same
circumstances. If a mixtur_e of 5.0 g of hydrogen and
-3
3
82
Matter and Energy
d. Milk of magnesia neutralizes stomach acid,
e. The steel in a car has rust spots.
10. g of methane is burned, and the heat released is trans-
fened to 500, g of water at 25 oC, what final temperature will be reached by the water?
f. A person
72. A 5.00-g sample of aluminum pellets and a 10.00-9 sam-
g. Sulfuric acid spilled on a laboratory notebook
ple of iron pellets are placed together in a dry test tube,
and the test tube is heated in a boiling water bath to 100.
oC. The mixture
of hot iron and aluminum is then poured
into 97.3 g of water at 22.5 oC. To what final temperature is the water heated by the metals?
50,0-9 sample of water at 100, oC is poured into a
50.0-9 sample of water at25 "C, What will be the final
temperature of the water?
73, A
j. Oil feels slippery.
\.
1.
heterogeneous.
a. the freshman ciass at your school
b.
salsa
c.
mashed potatoes
e. cream of mushroom soup
a
liquid
85. Classify, the following mixtures as homogeneou,r or
and a gas,
and randomly.
a. potting soil
d, window glass
b. white wine
"..-,.\c, your sock drawer
The factthat the substance copper(Il) sulfate pentahydrate
is bright blue is an example of a
propefiy.
_
78. The fact that the substance copper(Il) sulfate pentahydrate combines with ammonia in solution to form a new
compound is an example of a _
property.
(For Exercises 79-80) Solutions containing copper(Il) ions are
bright blue in color. When sodium hydroxide is added to such
a solution, a solid material forms that is colored a much paler
shade of blue than the original solution of copper(Il) ions.
79. The fact that a solution containing copper(Il) ions is
property,
bright blue is a
80. The fact that a reaction takes place when sodium hydroxide is added to a solution of copper(Il) ions is a
;-,:^.
86r'If it takes 4.5 J of energy to warm 5,0 g of aluminuin
'from
.
of melting and evaporation
of a substance.
_
83, -Classify the following as physical or chemical proper-
if a few drops of lemon juice
are added.
tempera-
b. Butter turns rancid if left exposed at room
d. 746.2kcal
162,4 cal
89. Convert the following numbers of jouleslkilojoules intc
kilocalories,
a. 52.18 kJ
c. 5.433
b, 4.298I
d, 455.9 kJ
x
103 J
90. Perform the followine conversions,
a. 5.442 x 104 J to illojoules
b. 5.442 X 104 J to calories
c..352.6 kcal to kilojoules
d. t7.24 kJ to kilocalories
9
1. Calculate the energy required to heat 25.0 g of gold fron
20.0 'C to 75,0 oC, Express your answer in joules, kile
joules, calories, and kilocalories.
92. Calculate the energy required (in joules) to heat 75 gai
ture.
c, Salad dressing
same temoerature interval.
b.
involve
is the process of making a chemical reaction
take place by passage of an electric cuffent through a
substance or solution.
t//
'''.-
88. Convert the followins numbers of calories/kilocalode.
into joules (J).
a. 44.21ca|
c. 3.721X 103 cal
-
81. The processes
25 oC to a certain higher temperature, then it wil;
J to warm 10. g of aluminum over thr
)iake
87. If it takes 103 J of energy to warfn a certain mass of iror
from 25 oC ro 50. oC, then it will take _
J tc
warm the same mass of iron from 25 'C to 75 oC.
property.
ties/changes,
a. Milk curdles
as
heterogeneous,
76, In gaseous substances, the individual molecules are re1atively (close/far apart) and are moving freely, rapidly,
changes in the
as
.
d, cream of tomato soup
75. Discuss the similarities and differences between
82.
Alcohol burns, forming carbon dioxide and water.
84, Classify the following mixtures as homogeneou,r or
the water-iron mixture?
.
page
causes the paper to char and disintegrate,
h. Sweat cools the body as it evaporates from the skin.
i, Aspirin reduces fever.
74. 425.0-9 sample of pure iron at 85 'C is dropped into
75 g of water at 20. oC. What is the final temperature of
77
is asphyxiated by breathing carbon, monox-
ide,
separates
into layers after
standing.
water from 25
'C to 39
oC,
DIREGTIONS - Classwork due end of period 4/21114:
Use 3pp (3 problems on each side of each of 2 papers for this assignment). On you
own piece of paper or scratch from the front of the room, put your name date and period
in the top right corner:
Your problems are in the Zum textbook: p. 81
Below I have specified the
problems to work, and given you hints to help in solving the problems.
You will be showing given, find, and circling the correct answer. All calculations must
be shown on your paper. Chart for specific heats needed in problems is on p.73
-82
67. a, b, c
68. hint: water is in the liquid state
69. hint: it is not enough to show answer, you must tell why
70.
86. hint: a and b are in the question in the book. l've given you help to figure a & b,
then l'm asking you something I made up in c
a. GIVEN: 4.5 J,5.0 g
FIND: ?
b. GIVEN: 10 g Al, AT is your answer from
Al
c. myquestiontoyou is: weretheJ
AT
a
,
FIND: ? J
in a&bproportional totheg in a&b (show
the 2 fractions side by side in your answer)?
87. hint: a and b are in the question in the book. I've given you help to figure a & b,
then I'm asking you something I made up in c
a. GIVEN: 103 J, AT = 50 - 25
FIND: ? g (Fe)
g
b, GIVEN: Fe (is ans from a), AT = 75 FIND: ? J
c, myquestiontoyou is: weretheJ in a & b proportional totheg in a & b (show
the 2 fractions side by side in your answer)?
88. a, b, c, d
"C
25'C
91.
ALL PROBLEMS ARE DUE AT THE END OF THE PERIOD
5
-Zum txt p.81 -82 CW 4121114
8 points = 100%
RUBRfC
Can have up to 4 pts extra credit
67. a, b, c You should see 3 problems, each having calculations
2 or more done = 1 pt
68. I pt if at least 2 done
69. 1 pt
79. 1 pt
86.
87.
a. 1 pt
b.1pt
c.1pt
a. 1 pt
b.1pt
c,1pt
88.
91.
1 pt if at least 2 done
1 pt
For full-credit paper$, or less than full credit, write
scores like this at top of page close to name like this:
sor*
For paper$ with Extra Credit, write $core$ like this at top
of page close to name like this:
B ..un
7z
E-
!6-