What is Calorimetry? Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction or physical change. We use a device called a calorimeter to do this.

What is Calorimetry?
Calorimetry is the process of measuring the amount of heat released or absorbed during a chemical reaction or physical change.

We use a device called a calorimeter to do this.

1. Calorimetry

2. Learning objectives:
By the end of this section, you will be able to:
Explain the technique of calorimetry
Calculateandinterpretheatandrelatedpropertiesusingtypical
calorimetrydata

3. Calorimetryisusedtomeasureamountsofheattransferredtoorfroma
substance.
Todoso,theheatisexchangedwithacalibratedobject(calorimeter).
Themeasurementofheattransferusingthisapproachrequiresthe
definitionofasystem(thesubstanceorsubstancesundergoingthe
chemicalorphysicalchange)and
…itssurroundings(theothercomponentsofthemeasurementapparatus
thatservetoeitherprovideheattothesystemorabsorbheatfromthe
system).

4. Knowledgeoftheheatcapacityofthesurroundings,andcarefulmeasurementsofthe
massesofthesystemandsurroundingsandtheirtemperaturesbeforeandafterthe
processallowsonetocalculatetheheattransferredasdescribedinthissection.
Acalorimeterisadeviceusedtomeasuretheamountofheatinvolvedinachemicalor
physicalprocess.
Forexample:
Whenanexothermicreactionoccursinsolutioninacalorimeter,theheatproducedby
thereactionisabsorbedbythesolution,whichincreasesitstemperature.
Whenanendothermicreactionoccurs,theheatrequiredisabsorbedfromthethermal
energyofthesolution,whichdecreasesitstemperature(Figure1).
Thetemperaturechange,alongwiththespecificheatandmassofthesolution,canthen
beusedtocalculatetheamountofheatinvolvedineithercase.

5. Figure 1.In a calorimetric determination, either
(a)anEXOTHERMIC processoccursandheat,q,isnegative,indicatingthatthermal
energyistransferredfromthesystemtoitssurroundings,or
(b)anENDOTHERMIC processoccursandheat,q,ispositive,indicatingthatthermal
energyistransferredfromthesurroundingstothesystem.
Exothermic = heat is released Endothermic = heat is absorbed

6. Commercialsolutioncalorimeters
arealsoavailable.Relatively
inexpensivecalorimetersoften
consistoftwothin-walledcupsthat
arenestedinawaythatminimizes
thermalcontactduringuse,along
withaninsulatedcover,handheld
stirrer,andsimplethermometer.
Moreexpensivecalorimetersused
forindustryandresearchtypically
haveawell-insulated,fullyenclosed
reactionvessel,motorizedstirring
mechanism,andamoreaccurate
temperaturesensor(Figure3). Figure 3.Commercial solution calorimeters range from
(a)simple, inexpensive models for student use to
(b)expensive, more accurate models for industry and research.

7. Constant-pressure calorimeter
Becausecalorimetryisusedtomeasuretheheatofareaction,it
isacrucialpartofthermodynamics.
Inordertomeasuretheheatofareaction,thereactionmustbe
isolatedsothatnoheatislosttotheenvironment.
Thisisachievedbyuseofacalorimeter,whichinsulatesthe
reactiontobettercontainheat.
Coffeecupsareoftenusedasaquickandeasytomake
calorimeterforconstantpressure.

8. Figure 2.A simple calorimeter
can be constructed from two
polystyrene cups. A
thermometer and stirrer extend
through the cover into the
reaction mixture.

9. •Thetemperaturechangeofthewaterismeasuredinthe
experimentandthespecificheatofwater(qsysten)canbeused
tocalculatetheheatabsorbedbythesurroundings(qsurroundings)
q
system= -q
surroundings
Where:
Q = heat
Theheatabsorbedbythesurroundingsisequal,butopposite
insign,totheheatreleasedbythesystem.Becausetheheat
changeisdeterminedatconstantpressure,theheatreleased
bythesystem(qsys)isequaltotheenthalpychangeH

10. qsystem= -qsurroundings
qmetal= -qwater
qsurr= m x Cs x T
Where:
q = heat
m = is the mass of the water
Cs = specific heat (for metal = 0.385 J/g ֯C)
Cs = specific heat (for water = 4.184 J/g ֯C)
T = Tfinal–Tinitial

11. Example
1. Pour hot coffee into a cup
2. the cup will become warm
3. because that hot coffee is
releasing its heat to the cup
4. So your system is releasing
its heat to its surrounding
Note:
Coffee = is the system
Styrocup = is the surrounding

12. Example
If you drop the
centavo into the
water, then the
centavo will release
its heat to the water
until they both have
the same final
temperature.
Temperature of
water is 25°C
Temperature of
centavo coin is
55 °C

13. Constant-volume Calorimeter
ConstantVolumeCalorimetry,alsoknowas
bombcalorimetry,isusedtomeasuretheheatof
areactionwhileholdingvolumeconstantand
resistinglargeamountsofpressure.
Bombcalorimetryisusedtomeasuretheheat
thatareactionabsorbsorreleases,andis
practicallyusedtomeasurethecaloriecontentof
food.
Abombcalorimeterisatypeofconstant-volume
calorimeterusedtomeasureaparticular
reaction’sheatofcombustion.

14. Forinstance,ifwewereinterestedindeterminingthe
heatcontentofasushiroll,forexample,wewouldbe
lookingtofindoutthenumberofcaloriesitcontains.
Inordertodothis,wewouldplacethesushirollina
containerreferredtoasthe“bomb”,sealit,andthen
immerseitinthewaterinsidethecalorimeter.
Then,wewouldevacuatealltheairoutofthe
bombbeforepumpinginpureoxygengas(O
2).After
theoxygenisadded,afusewouldignitethesample
causingittocombust,therebyyieldingcarbon
dioxide,gaseouswater,andheat.
Assuch,bombcalorimetersarebuilttowithstandthe
largepressuresproducedfromthegaseousproducts
inthesecombustionreactions.

15. Bomb calorimetry Bomb calorimeter
A schematic representation of a bomb calorimeter used
for the measurement of heats of combustion.
The weighed sample is placed in a crucible, which in turn
is placed in the bomb.
The sample is burned completely in oxygen under
pressure.
The sample is ignited by an iron wire ignition coil that
glows when heated.
The calorimeter is filled with fluid, usually water, and
insulated by means of a jacket.
The temperature of the water is measured with the
thermometer.
From the change in temperature, the heat of reaction can
be calculated.

17. Problem Solving #1
•What is the specific heat of aluminium if the temperature of a 28.4gsample of
aluminium is increased by 8.1ºCwhen 207 J of heat is added?
•Given:
M = 28.4 g
T = 8.1 ºC
Q = 207 J
Required = Cs = ?
•Formula: q = mx Csx T
Cs= q / (m T)
= 207 J / 28.4 g x 8.1 ºC
= 207 J / 230.04 gºC
Cs= 0.90 J/gºC

18. Problem Solving #2
•Howmuchheatmustbeaddedtoa8.21gsampleofgoldto
increaseitstemperatureby6.2ºC?Thespecificheatofgoldis0.13
J/gºC.
•Given:
•M = 8.21 g
•T = 6.2 ºC
•Cs = 0.13 J /gºC
•Reqd: q=?
•Solution: q= m x Csx T

19. •Given:
m = 8.21 g
T = 6.2 ºC
Cs = 0.13 J /gºC
•Reqd: q=?
•Solution: q= m x Csx T
= 8.21 g x 0.13 J/gºCx 6.2 ºC
q = 6.62 J

20. Problem Solving #3
5.0gofcopperwasheatedfrom20°Cto80°C.How
muchenergywasusedtoheatCu?(Specificheat
capacityofCuis0.092cal/g.°C)
Given:
m = 5.0 g
T
f= 80 ºC
T
i= 20 ºC
Cs = 0.092J /gºCor 0.092 cal/gºC
Reqd: q=?

21. Solution:
q= m x Csx T
= 5.0 g x 0.092 J/gºCx (80ºC -20 ºC)
= 5.0 g x 0.092 J/gºCx 60 ºC
q = 27.6 J or cal

22. Problem Solving #4
Howmuchheatisabsorbedbya20ggraniteboulderas
energyfromthesuncausesitstemperaturetochange
from10°Cto29°C?(Specificheatcapacityofgraniteis
0.1cal/g.°C)
Given:
m = 20 g
T
f= 29 ºC
T
i= 10 ºC
Cs = 0.1J /gºCor 0.1 cal/gºC
Reqd: q=?

23. Solution:
q= m x Csx T
= 20 g x 0.1J/gºCx (29ºC -10 ºC)
= 20 g x 0.1J/gºCx 19 ºC
q = 38 J or cal

24. Problem Solving #5
Howmuchheatisreleasedwhen30gofwaterat96°C
coolsto25°C?Thespecificheatofwateris1cal/g°C.
Given:
m = 30 g
T
f= 25 ºC
T
i= 96 ºC
Cs = 1J /gºCor 1 cal/gºC
Reqd: q=?

25. Solution:
q= m x Csx T
= 30 g x 1J/gºCx (25 ºC -96 ºC)
= 30 g x 1 J/gºCx (-71 ºC)
q = -2130 J or cal
The negative shows that the energy
released from the water.

26. Problem Solving #6
Ifa3.1gringisheatedusing10.0calories,itstemperature
rises17.9°C.Calculatethespecificheatcapacityofthe
ring.
Given:
m = 3.1 g
T
f= 17.9 ºC
q = 10.0 cal
Reqd: Cs=?

27. Solution:

28. Problem Solving #7
Thetemperatureofasampleofwaterincreasesfrom
20°Cto46.6°Casitabsorbs5650caloriesofheat.What
isthemassofthesample?(Specificheatofwateris1.0
cal/g.°C)
Given:
Cs = 1 cal/gºC
T
f= 46.6 ºC
T
i= 20.0 ºC
q = 5650 cal
Reqd: m=?

29. Solution:

30. •https://www.youtube.com/watch?v=WatGC0bw8jw
•Simple calorimetry experiment