Thermochemistry Practice Test - General Chemistry
Ansner Key
Name
Hr
Date
Cwstar 4. 184 J/a'c
AHfueion = 6.01 kJ/mol
Cice =2,03 J/ C
Cvapor =2.01 J/q C
AHvop = 40.65 kJ/mol
q=mcAT
1 What mass of liquid water requires 55 J to go from 13 °C to 72 °C ?
q-mcaT
553 =m: 4.184 ThC"59C
9- 55J
55T- 241b. 86 m
C= 4.13477
m=o,22g
AT=(72c-j3°c) 54°c
2. It takes 230.4 J to heat 32 grams of silver from 30°C to 60 °C. What is the specific hedt in Joules/g°C?
qemcaT
230,47 - 324:c" 30°C
9=230,4T
230.43- 4b0gc c
ma32
C=?
AT: b0°C -30°c:30°c
3. When 385.6 J.of heat is added to 5.7g of vinegar at 22°C, the temperature increases to 55°C. What is the
specific heat of the vinegar?
385.6T=5.74c· 33c
335(63= 138.1qCc
q=mcaT
q=395.6T
me57
C:?
C=2,053|
AT: 55°C - 22°c33c
4. Calculate the energy transferred when 7.9g of ice is melted at 0.0°c. Is energy absorbed or released?
qnaH
90:43mol o.oIkT/mol
q=?
0.438mol
energy is absorbed
AHsb.GikJ/mol
5. Astudent takes a 62.05g sample of an unknown metal and places it into boiling water (100°C). She then
removes the metal and places it in 75gof cool water initially at 25.5°C. If the final temperature of the
water and the metal is 30.7°C, what is the specificheat of the
metal?
q2 meaT
q= mcaT
water
3
9: -1b3.76
m=759
Metal mab2.o5
AT:(30.7°-25.5°c)=5,2°c
q=?
AT: (30.7-lo0°c)-64.3c
-Ib31,76 = b2.056 c61.3°c
q=l631.76 -|63.7
water
3-metal
- I631.7b = ~300.07 c
|Ce 0.374 TC
6. Calculate the energy transferred when 12. 8gof water vapor condenses on a soda con at 100 0°C. Is energy
absorbed or released?
q20.7l mol 40.65kT/ol
qnaH
n: 12.8al Imol
: 0,7|mol
AH 40.45k5/mol
Tonert is absorbed|
vap
7. Calculate the energy transferred in joules when 55.9g of liquid water decreases from 7.0°C to0.0°C and
then freezes at 0.0°c. Was energy absorbed or released? fn Hs
9-mcT
q:?
n= 55.9| Imol :3.lmoi
q= 1437.20 J
m=5s.4g
C=
q:3.Jmal-(o.o1 kJlmol
4= 18.63 k3 ||oooT
AT7°c
toe lkt
1s63/T
is releasecl
ondrgy
8. Calculate the energy transferred in joules when 36g of liquid water rises from 42°C to 100.0°C and then
|b37.2+ |8631T -20268.2T|
boiled. Was energy absorbed or released?
qnaHae
qmeAT
cz4.1343lgo
973b. 25
OHuap
+ 8736.23
= Z.00mol
0. L5KTImol
q2 mal. 0.65kT}mol = YI.3kJ
energy is absorbed]
lq-4003bi2
9. How much energy in joules does it take to raise 39.7g of ice at 0.0°C to 100.0°C and then boil?
qmeaT"
q2naH
qnAH
n=39.74] Imol 2.20 mmol
AHb.o1kSlmo)
fus
Z.2mol.b.o|kS|molz
13.22 kS] loo0S =13222J
9-?
n:2.20ml
mo39.79
co44l
0T=\00C
At = 40.6 k3m ol
vap
4-lbb|O.48J
:$943OS
13222+1blblo484 sq430 = 14202.48T
10. How much energy in kI does 42g of ethanol gas lose when it lowers from 95°C to 78C and then becomes
liquid? The specific heat of ethanol gas is 2.428/g°c. The AHvep of ethanol is 0.826kJ/g
4=meaT
gnaH
AT=45°c -78°c)=I7c
431.73ES
-=I.73kJ
41733.5
1,73+34.69=36.42 kJ
0
