Thermochemistry Problem Practice and Solutions
Answers to the 12 Thermochem
Questions you practiced while
walking around
Grade yourself harshly, units
and SF count dearly.
1. How much energy in joules, is required to
melt 145 grams of solid ice at 273 K into
liquid water?
q = mH
F
= (145g)(334 J/g)
= 48,400 J with 3 SF
2. Convert 1895 C into joules.
1895 C
1
X
1000 cal
1 C
= 1,895,000 cal
1,895,000 cal
1
X
4.18 J
1 cal
= 7,921,000 J
with 4 SF
3. How much energy in joules, is release
when 432 grams of steam condenses
into water?
q = mH
V
= (432g)(2260 J/g)
= 976,000 J with
3 SF
4. Copy down the 2 correct math
expressions
C of Cu > C of H
2
O H
V
= H
F
H
V
< H
F
C of Cu < C of H
2
O
C
ICE
< C
WATER
C
ICE
> C
WATER
5. How much energy in joules, is
required to raise the temperature of
75.0 grams of water from 34.5°C
to 45.8°C?
q = mC∆T = (75.0g)(4.18J/g
·K)(11.3 K)
= 3542.55 = 3540 J
with 3 SF
6. Copy down the 2 correct math expressions
H
V
> H
F
H
V
= H
F
H
V
< H
F
KE > PE
C
ICE
= C
WATER
C
ICE
< C
WATER
7. How much energy in joules, is required to
raise the temperature of 75.0 grams of
copper from 44.5°C to 55.8°C?
(C
Cu
= 0.391 J/g·K)
q = mC∆T =
(75.0g)(0.391J/g
·K)(11.3 K)
= 331.3725 = 331 J
with 3 SF
8. Convert the number of joules in your
answer to question #7 into kilojoules and
into calories (small “c”)
331 J
1
X
1 kJ
1000 J
=
0.331 kilojoules
331 J
1
X
1 cal
4.18 J
=
79.2 cal
9. At what temperature in CENTIGRADE
would aluminum melt?
K = C + 273
933 = C +273
-273 = -273
660°C
10. The H
F
for aluminum is 403 J/g, which is why you
can’t melt aluminum in your mouth. A soda can
might mass at 48.2 grams. How much energy in
joules is needed to melt that can into liquid?
(
assume ∆T = 0
)
q = mH
F
= (48.2g)(403 J/g)
= 19,424.6
= 19,400 J
with 3 SF
11. When 454 g bismuth changes temperature
from 273 K to 296 K, it takes 1284 Joules.
What is the C of Bi?
q = mC∆T
1284 J = (454g)(C
Bi
)(23.0K)
1284 J
10,442 g
·K
= C
Bi
=
0.123 J/g
·K
The 13
th
Amendment
to the Constitution of the United States
"Neither slavery nor involuntary servitude,
except as a punishment for crime whereof
the party shall have been duly convicted,
shall exist within the United States, or any
place subject to their jurisdiction."
12. The C
Fe
= 0.45 J/g·K. When 2005 Joules is
able to change the temperature of iron by
67.5 Kelvin, what is the mass of this iron?
q = mC∆T
2005 J = (m)(0.45J/g
·K)(67.5K)
2005 J
(30.375J/g)
The “K’s” cancel out
= 66.0 g with 3 SF
the “J’s” cancel out, the g of the denominator of
the denominator jumps to the numerator
Practice and solutions for thermochemistry problems involving energy calculations, temperature conversions, and phase changes. Includes calculations for melting ice, converting temperature to joules, and determining energy required for heating substances.
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Presentation Transcript
Answers to the 12 Thermochem Questions you practiced while walking around Grade yourself harshly, units and SF count dearly.
1. How much energy in joules, is required to melt 145 grams of solid ice at 273 K into liquid water? q = mHF = (145g)(334 J/g) = 48,400 J with 3 SF
2. Convert 1895 C into joules. X1000 cal 1 C 1895 C 1 = 1,895,000 cal X 4.18 J 1 cal 1,895,000 cal 1 = 7,921,000 J with 4 SF
3. How much energy in joules, is release when 432 grams of steam condenses into water? q = mHV = (432g)(2260 J/g) = 976,000 J with 3 SF
4. Copy down the 2 correct math expressions C of Cu > C of H2O HV = HF HV < HF C of Cu < C of H2O CICE < CWATER CICE > CWATER
5. How much energy in joules, is required to raise the temperature of 75.0 grams of water from 34.5 C to 45.8 C? q = mC T = (75.0g)(4.18J/g K)(11.3 K) = 3542.55 = 3540 J with 3 SF
6. Copy down the 2 correct math expressions HV > HF HV < HF HV = HF KE > PE CICE = CWATER CICE < CWATER
7. How much energy in joules, is required to raise the temperature of 75.0 grams of copper from 44.5 C to 55.8 C? (CCu = 0.391 J/g K) q = mC T = (75.0g)(0.391J/g K)(11.3 K) = 331.3725 = 331 J with 3 SF
8. Convert the number of joules in your answer to question #7 into kilojoules and into calories (small c ) 1 kJ 1000 J 331 J 1 = 0.331 kilojoules X 1 cal 4.18 J 331 J 1 = 79.2 cal X
9. At what temperature in CENTIGRADE would aluminum melt? K = C + 273 933 = C +273 -273 = -273 660 C
10. The HF for aluminum is 403 J/g, which is why you can t melt aluminum in your mouth. A soda can might mass at 48.2 grams. How much energy in joules is needed to melt that can into liquid? (assume T = 0) q = mHF = (48.2g)(403 J/g) = 19,424.6 = 19,400 J with 3 SF
11. When 454 g bismuth changes temperature from 273 K to 296 K, it takes 1284 Joules. What is the C of Bi? q = mC T 1284 J = (454g)(CBi)(23.0K) 1284 J 10,442 g K = CBi = 0.123 J/g K
The 13th Amendment to the Constitution of the United States "Neither slavery nor involuntary servitude, except as a punishment for crime whereof the party shall have been duly convicted, shall exist within the United States, or any place subject to their jurisdiction."
12. The CFe = 0.45 J/gK. When 2005 Joules is able to change the temperature of iron by 67.5 Kelvin, what is the mass of this iron? q = mC T 2005 J = (m)(0.45J/g K)(67.5K) 2005 J (30.375J/g) = 66.0 g with 3 SF the J s cancel out, the g of the denominator of the denominator jumps to the numerator The K s cancel out
