Energy

1
Energy Chemical Change
-_______ is the ability to do ______ or produce
_____
energy
work
heat
I. Potential Energy
potential
position
-__________ energy is the energy of ________,
like the water stored behind the dam, or the
energy of ____________ of a __________, which
depends on the _____ of ______, the _______ and
_____ of ______ joining the ______ together,
and the way the ______ are _________
composition
substance
type
atoms
number
type
bonds
atoms
atoms
arranged
chemical potential energy for ethyne
(acetylene) 1665 kJ/mol
2
Energy Chemical Change
I. Potential Energy
H H
74
436
The ____ of all the _____ _____________ _________
for all ______ in a ________ determines the
chemical _________ _______ for that __________
sum
C C
154
348
bond
dissociation
F F
142
159
energies
Cl Cl
199
243
bonds
molecule
Br Br
228
193
I I
151
267
potential
H C
413
109
energy
H F
92
568
molecule
H Cl
127
432
H Br
141
366
161
298
H I
134
614
839
120
945
110
chemical potential energy for Carbon
tetrachloride 1320 kJ/mol
C F
488
135
330
C Cl
177
3
Energy Chemical Change
II. Kinetic Energy
-__________ energy is the energy of ________.
When the gates of the dam open, the _________
energy of the stored water is converted to
_________ energy and used to do the ______ of
generating ___________
kinetic
motion
potential
kinetic
work
electricity
-the ________ energy of a __________ is directly
related to the _______ ________ of its _________
and is ______________ to its ____________
kinetic
substance
random
motion
particles
proportional
temperature
4
Energy Chemical Change
III. Specific Heat
-the _________ ______ of a substance is the
amount of ______ required to raise the
____________ of ____ _____ of that substance
____ _________ _______
specific
heat
heat
temperature
one
gram
one
Celsius
degree
-the _________ ______ of ______ is ____
________, or _____ J/gC
specific
heat
water
one
calorie
4.184
A. Calculating Specific Heat
c
q

?T
x
m
x
q

the heat absorbed or released
c

the specific heat of the substance
m

the mass of the sample in grams
?T

the change in temperature in C
5
Energy Chemical Change
III. Specific Heat
A. Calculating Specific Heat
If the temperature of 34.4 grams of ethanol
increases from 25.0C to 78.8C, how much heat
has been absorbed by the ethanol?
q

the heat absorbed or released
c

the specific heat of the substance
2.44 J/gC

m

the mass of the sample in grams

34.4 g
?T

the change in temperature in C

53.8C
q
x
x

2.44 J/gC
34.4 g
53.8C
q
4510 J

6
Energy Chemical Change
III. Specific Heat
A. Calculating Specific Heat
A 4.50-gram nugget of pure gold absorbed 276
joules of heat. What was the final temperature
of the gold if the initial temperature was 25.0C?
q

the heat absorbed or released

276 J
c

the specific heat of the substance
0.129 J/gC

m

the mass of the sample in grams

4.50 g
?T

the change in temperature in C

Tfinal
-
Tinitial
x
x

0.129 J/gC
4.50 g
(Tfinal - 25.0C)
276 J
Tfinal
501C

7
Energy Chemical Change
III. Specific Heat
A. Calculating Specific Heat
A 155-gram sample of an unknown substance was
heated from 25.0C to 40.0C. In the process,
the substance absorbed 5676 joules of energy.
What is the specific heat of the substance, and
what is the substance?
q

the heat absorbed or released

5676 J
c

the specific heat of the substance
m

the mass of the sample in grams

155 g
?T

the change in temperature in C

40.0C
-
25.0C
x
x

c
155 g
15.0C
5676 J
c
2.45 J/gC

8
Energy Chemical Change
III. Specific Heat
A. Calculating Specific Heat
How much heat, in calories, is absorbed by a 2000
kilogram granite boulder as it is warmed from
25.0C to 44.0C?
q
x
x

0.803 J/gC
2.000 x 106 g
19.0C
q
3.06 x 107 J
x
1.00 cal

4.184 J
q

7.31 x 106 cal
A 100.0-gram ingot of silver absorbed 1182 joules
of heat. What was the final temperature of the
silver if the initial temperature was 25.0C?
x
x

0.235 J/gC
100.0 g
(Tfinal - 25.0C)
1182 J
Tfinal
75.3C

9
Energy Chemical Change
III. Measuring Heat
-a _____________ is an insulated device used for
measuring the amount of _____ _________ or
_________ during a ________ or ________
reaction, usually by measuring the __________
change of a known _____ of ______
calorimeter
heat
absorbed
released
chemical
physical
temperature
mass
water
What is the specific heat of an unknown metal,
and what is the unknown metal, if a 49.4 gram
sample of the metal is heated to an initial
temperature of 115.0C and placed in 125 grams of
water, raising the temperature of the water from
25.6C to 29.3C and lowering the temperature of
the metal from 115.0C to 29.3C?
qwater
x
x

4.184 J/gC
125 g
3.7C
qwater
1900 J

cmetal

x
mmetal
x
?Tmetal
x
x

c
49.4 g
85.7C
1900 J
cwater
?Twater
x
mwater
x
c
0.45 J/gC

(Iron)
10
Energy Chemical Change
III. Measuring Heat
-calorimetry lab
1. Hypothesis
How can we measure the specific heat capacity of
an unknown sample?
2. Prediction
3. Gather Data
A. Safety
The hot water and metal masses immersed in the
hot water will be hot enough to cause burns. Use
caution. Handle masses with tongs. Goggles and
aprons mandatory.
B. Procedure
1. With your partner, obtain a metal sample and
record the mass and the type of metal (C,
Z, T, or S).
2. Using a 100-mL graduated cylinder, measure a
mass of water just enough to cover the
sample in the calorimeter.
11
Energy Chemical Change
III. Measuring Heat
-calorimetry lab
3. Gather Data
B. Procedure
12
Energy Chemical Change
III. Measuring Heat
-calorimetry lab
3. Gather Data
B. Procedure
3. Record the mass of the water and pour it into
the calorimeter.
4. Use a thermometer to determine the initial
temperature of the water in the calorimeter.
Record.
5. Immerse the mass of metal in the hot water
bath for at least 1 minute. Take note of
the temperature of the water bath and record
as the initial temperature of the metal.
6. Use tongs to remove the mass from the hot
water bath. Shake mass to remove drops of
hot water and immediately immerse the mass
in the water of the calorimeter
7. Cover the calorimeter and insert the
thermometer. Stir the water in the
calorimeter constantly.
13
Energy Chemical Change
III. Measuring Heat
-calorimetry lab
3. Gather Data
B. Procedure
8. Record the final (highest) temperature of the
water in the calorimeter.
4. Analyze Data
use the data gathered from the procedure to
calculate the specific heat of the unknown metal
cmetal
cwater

x
mmetal
x
?Twater
x
mwater
x
?Tmetal
5. Draw Conclusions
using the analysis of the data, answer the
question of the hypothesis
14
Energy Chemical Change
IV. Enthalpy (Heat) of Reaction
-_________ is the _____ of a system at a
constant _________, while the _________ of
________, or _____ is the ___________ between
the _________ of the substances at the
__________ of the reaction and the substances
at the ____ of the reaction
enthalpy
heat
pressure
enthalpy
reaction
?Hrxn
difference
enthalpy
beginning
end
-a ______________ __________ is a balanced
chemical equation that includes the _______
_____ of all reactants and products and the
energy change, expressed as the _______ in
________, or ____
thermochemical
equation
physical
states
combustion reactions are always exothermic and
have ?Hrxn values
change
enthalpy
?H
2C8H18(s)
16CO2(g)

25O2(g)

18H2O(l)

-10,942 kJ
15
Energy Chemical Change
IV. Enthalpy (Heat) of Reaction
Referring to Table 16-5 on p. 501 of your text
write a complete balanced thermochemical equation
for the combustion of sucrose, hydrogen, and
ethanol.
1C12H22O11 (s)
12CO2(g)

12O2(g)

11H2O(l)

-5644 kJ
2H2 (g)

1O2(g)
2H2O(l)

-572 kJ
1C2H5OH (l)
2CO2(g)

3O2(g)

3H2O(l)

-1367 kJ
16
Energy Chemical Change
V. Changes of State
-physical processes, such as ________ in ______,
also absorb or release _____
changes
state
heat
-the amount of _____ required to _________ one
_____ of ______ into ____ is called that
substances ______ ______________ of
___________, or _____
heat
vaporize
mole
liquid
gas
molar
enthalpy (heat)
?Hvap
vaporization
-the amount of _____ required to ____ one
_____ of ______ into _______ is called that
substances ______ ______________ of ______, or
_____
heat
melt
mole
solid
liquid
molar
enthalpy (heat)
?Hfus
fusion
17
Energy Chemical Change
V. Changes of State
-the amount of _____ that must be _________ in
the ___________ process of ____________ is the
same amount of _____ that is ________ in the
___________ process of ___________, or _____
______
heat
absorbed
endothermic
vaporization
heat
released
exothermic
condensation
?Hvap
-?Hcond
-the amount of _____ that must be _________ in
the ___________ process of ________ is the same
amount of _____ that is ________ in the
___________ process of ___________, or _____
______
heat
absorbed
endothermic
melting
heat
released
exothermic
solidification
?Hfus
-?Hsolid
18
Energy Chemical Change
V. Changes in State
Referring to Table 16-6 on p. 502 of your text
write a thermochemical equation for the
condensation of ethanol, the solidification of
methanol, and the vaporization of ammonia.
1C2H5OH (g)
?Hcond -38.6 kJ
1C2H5OH (l)
1CH3OH (l)
?Hsolid -3.22 kJ
1CH3OH (s)
1NH3 (l)
?Hvap 23.3 kJ
1NH3 (g)
19
Energy Chemical Change
VI. Calculating Energy Releases in a Reaction
What amount of heat, in kilojoules, is required
to melt 25.7 grams of solid methanol at the
melting point of methanol?
1 mole CH3OH
3.22 kJ
25.7 g CH3OH
x
_____________

2.58 kJ
x
_____________
32.042 g CH3OH
1 mole CH3OH
What amount of heat, in kilojoules, is evolved
when 275 grams of ammonia gas condenses to a
liquid at the boiling point of ammonia?
1 mole NH3
23.3 kJ
275 g NH3
x
___________

376 kJ
x
_____________
17.031 g NH3
1 mole NH3
What mass, in grams, of methane must be burned in
order to produce 12,880 kilojoules of heat?
1 mole CH4
16.043 g CH4
12,880 kJ
x
___________

232 g CH4
x
_____________
891 kJ
1 mole CH4
20
Energy Chemical Change
VII. Hesss Law
-some __________ ___________ occur slowly over
millions of years, while others occur under
conditions difficult to duplicate in the
_________, and others occur accompanied by the
production of many other _________
chemical
reactions
laboratory
products
-_______ ____ states that ____ or _____
thermochemical equations can be added together
to produce a ______ __________, and the ____ of
the _________ __________ for the individual
__________ is the _________ _______ for the
______ _________
Hesss
Law
two
more
The conversion of diamond (above) to graphite
(below) takes millions of years
final
equation
sum
enthalpy
changes
reactions
enthalpy
changes
final
reaction
21
Energy Chemical Change
VII. Hesss Law
What is the enthalpy change, in joules, for the
decomposition of Hydrogen peroxide?
2H2O2 (l)
1O2(g)

2H2O(l)
?H ? kJ
Hydrogen peroxide is made by the synthesis
reaction of hydrogen and oxygen
1H2 (g)

1O2(g)
1H2O2(l)
?H -187.8 kJ
So
2H2O2 (l)
2H2(g)

2O2(g)
?H 375.6 kJ
Water is made by the synthesis reaction of
hydrogen and oxygen
2H2 (g)

1O2(g)
2H2O(l)
?H -571.660 kJ
So the final equation for the decomposition is
like the sum of the equations for the individual
decomposition and synthesis reactions
22
Energy Chemical Change
VII. Hesss Law
Add the individual equations together and cancel
the common terms
2H2O2 (l)
2H2(g)

2O2(g)
?H 375.6 kJ
2H2 (g)

1O2(g)
2H2O(l)
?H -571.660 kJ

2H2O2 (l)
2H2O(l)
1O2(g)

?H -196.1 kJ
What is the enthalpy change, in joules, for the
following single replacement reaction
3MnO2 (s)
2Al2O3(s)

4Al(s)

3Mn(s)
?H ? kJ
If
4Al (s)
2Al2O3(s)

3O2(g)
?H -3351.4 kJ
and
1Mn (s)
1MnO2(s)

1O2(g)
?H -520.03 kJ
23
Energy Chemical Change
VII. Hesss Law
First, if
1Mn (s)
1MnO2(s)

1O2(g)
?H -520.03 kJ
then
3Mn (s)
3MnO2(s)

3O2(g)
?H 1560.1 kJ
finally
3Mn (s)
3MnO2(s)

3O2(g)
?H 1560.1 kJ

4Al (s)
2Al2O3(s)

3O2(g)
?H -3351.4 kJ
3MnO2 (s)
2Al2O3(s)

4Al(s)

3Mn(s)
?H -1791.3 kJ
24
Energy Chemical Change
VII. Hesss Law
What is the enthalpy change, in joules, for the
following reaction
2CO (g)
2CO2(g)

2NO(g)

1N2(g)
?H ? kJ
2CO (g)
2C(s)
?H 220.050 kJ

1O2(g)
2C (s)
2CO2(g)

1O2(g)
?H -787.018 kJ
2CO (g)
2CO2(g)

1O2(g)
?H -565.968 kJ
2NO (g)
1N2(g)
?H -180.5 kJ

1O2(g)

2CO (g)
2CO2(g)

2NO(g)

1N2(g)
?H -746.5 kJ
What is the enthalpy change, in joules, for the
following reaction
1Sn (s)
1SnCl4(l)

2Cl2(g)
?H ? kJ
1Sn (s)
1SnCl2(s)

1Cl2(g)
?H -325 kJ
1SnCl2 (g)
1Cl2(g)
?H -186 kJ

1SnCl4(l)

1Sn (s)
1SnCl4(l)

2Cl2(g)
?H -511 kJ
25
called the standard enthalpy of formation,
represented by dHof. Unless specified, the
temperature is 298 K.
Energy Chemical Change
VIII. Standard Enthalpy (Heat) of
Formation
-________ _________ of __________, or _____, is
the ________ in _________ that accompanies the
__________ of ___ ____ of a _________ in its
__________ ______ from its constituent _________
in their __________ ________
standard
enthalpy
formation
?Hf0
change
enthalpy
formation
one
mole
compound
standard
state
elements
standard
states
-_________ and __________ are in their _________
_______ at _____________ of ________ and _____
or _____
elements
compounds
standard
states
1 atmosphere
pressure
25C
298 K
3 2
S (s)
SO3(g)

O2(g)
?Hf0 -454.51 kJ
1
1
-formation reactions with negative _____ values
are __________, and formation reactions with
positive _____ values are ___________
?Hf0
exothermic
?Hf0
endothermic
1 2
N2 (g)
NO2(g)

O2(g)
?Hf0 33.18 kJ
1
1
26
Energy Chemical Change
IX. Hesss Law Calculation Using Standard
Enthalpies of Formation
What is the enthalpy change, in kilojoules, for
the following reaction
1H2S (g)
2HF(g)

4F2(g)

1SF6(g)
?H0rxn ? kJ
1 2
1 2
H2 (g)
HF(g)

F2(g)
?Hf0 -271.1 kJ
1
S (s)
SF6(g)

F2(g)
?Hf0 -1220.5 kJ
1
1
3
H2 (g)
H2S(g)

S(s)
?Hf0 -20.63 kJ
1
1
1
H2 (g)
HF(g)

F2(g)
?Hf0 -542.2 kJ
2
1
1
S (s)
SF6(g)

F2(g)
?Hf0 -1220.5 kJ
1
1
3
H2 (g)
H2S(g)

S(s)
1
1
1
?Hf0 20.63 kJ
1H2S (g)
2HF(g)

4F2(g)

1SF6(g)
?H0rxn -1742.1 kJ
27
Energy Chemical Change
IX. Hesss Law Calculation Using Standard
Enthalpies of Formation
What is the enthalpy change, in kilojoules, for
the following reaction
1CH4 (g)
1CO2(g)

2O2(g)

2H2O(l)
?H0rxn ? kJ
C (s)
CO2(g)

O2(g)
?Hf0 -393.509 kJ
1
1
1
H2 (g)
H2O(l)

O2(g)
?Hf0 -571.660 kJ
2
2
1
H2 (g)
CH4(g)

C(s)
1
2
1
?Hf0 74.81 kJ
1CH4 (g)
1CO2(g)

2O2(g)

2H2O(l)
?H0rxn -890.36 kJ
?H0rxn

S ?Hf0 (products)
-
S ?Hf0 (reactants)
28
Energy Chemical Change
IX. Hesss Law Calculation Using Standard
Enthalpies of Formation
What is the enthalpy change, in kilojoules, for
the following reaction (See Appendix C, Table
C-13, on p. 921)
1CaCO3 (s)
1CO2(g)

1CaO(s)
?H0rxn ? kJ
?H0rxn

S ?Hf0 (products)
-
S ?Hf0 (reactants)
?Hf0 (CO2) -393.509 kJ
?Hf0 (CaO) -635.1 kJ
?Hf0 (CaCO3) -1206.9 kJ
?H0rxn

(
-393.509 kJ

-635.1 kJ
)
-
(
-1206.9 kJ
)

178.3 kJ
29
Energy Chemical Change
IX. Hesss Law Calculation Using Standard
Enthalpies of Formation
What is the enthalpy change, in kilojoules, for
the following reaction (See Appendix C, Table
C-13, on p. 921)
1CH4 (g)
1CCl4(l)

2Cl2(g)

2H2(g)
?H0rxn ? kJ
?H0rxn

S ?Hf0 (products)
-
S ?Hf0 (reactants)
?Hf0 (CCl4) -128.2 kJ
?Hf0 (H2) 0 kJ
?Hf0 (CH4) -74.81 kJ
?Hf0 (Cl2) 0 kJ
?H0rxn

(
-128.3 kJ

0 kJ
)
-
(
-74.81 kJ
)

-53.5 kJ

0 kJ
30
Energy Chemical Change
IX. Hesss Law Calculation Using Standard
Enthalpies of Formation
Given the enthalpy change for the reaction,
calculate the standard enthalpy of formation for
Sodium carbonate, in kilojoules (See Appendix C,
Table C-13, on p. 921)
2NaHCO3 (s)
1Na2CO3(s)

1CO2(g)
?H0rxn 135.6 kJ
1H2O(g)

?H0rxn

S ?Hf0 (products)
-
S ?Hf0 (reactants)
?Hf0 (Na2CO3) ? kJ
?Hf0 (CO2) -393.509 kJ
?Hf0 (H2O) -241.818 kJ
?Hf0 (NaHCO3) -1902 kJ
135.6 kJ

(
?Hf0 (Na2CO3)

-393.509 kJ
)
-
(
-241.818 kJ
)

-1902) kJ

-1131 kJ
?Hf0 (Na2CO3)
31
Energy Chemical Change
IX. Hesss Law Calculation Using Standard
Enthalpies of Formation
Given the enthalpy change for the reaction,
calculate the standard enthalpy of formation for
Iron(III) oxide, in kilojoules (See Appendix C,
Table C-13, on p. 921)
4FeS (s)
7O2(g)

2Fe2O3(s)
?H0rxn -2435.7 kJ
4SO2(g)

?H0rxn

S ?Hf0 (products)
-
S ?Hf0 (reactants)
?Hf0 (Fe2O3) ? kJ
?Hf0 (SO2) -1187.32 kJ
?Hf0 (FeS) -400.0 kJ
?Hf0 (O2) 0 kJ
-2435.7 kJ

(
?Hf0 (Fe2O3)

-1187.32 kJ
)
-
(
-400.0 kJ
)

0 kJ
-1648.4 kJ
?Hf0 (Fe2O3)
-824.2 kJ


2