Guard your heart above all else, for it determines the course of your life.
1
Some like it hot !
Or
Calorimetry
Alexandra Khvan, Andy Watson
• What is calorimetry?
• How old is calorimetry? Very old but gold! First
calorimeters appeared before Thomas Johann Seebeck
invented the thermocouple
• What do we want to find out?
• What do we measure?
• How can we measure? (different types of
calorimeters)
• Is it easy? Yes and NO at the same time
• How long do calorimeters live?
They live and produce good results much longer than the
people who created them
3
What do we count calories for?
Answer taken from presentation of Prof Alex Navrtosky US Davis
• They are fascinating
– Energetics whisper secrets of the strength of chemical bonds
– Entropies sing of vibrating atoms, moving electrons, and
structural disorder
– Systematics have predictive power
• They pay
– thermodynamic data are essential to good materials processing
– Environmental science needs thermodynamics, both for issues of
stability and as a starting point for kinetics
– Mineralogy, petrology, metallurgy and deep Earth geophysics
need thermodynamic data.
4
What do we want to find out?
•
•
•
•
Enthalpies of formation (reaction)ΔfH, ΔrH
Heat capacities Cp
Enthalpies of mixing (solution phases)ΔHmix
Enthalpies of transformation ΔHtr
5
But what do we actually measure?
1780
Pierre-Simon Laplace
Antoine Laurent de Lavoisier
Calorimeter is an instrument for the measurement of released or absorbed heat during
some physical, chemical or biological process
6
Calorimetry
Measure the amount of heat change
Cannot measure enthalpy directly.
»Isoperibol calorimetry
Measure the temperature change (Tc),
Ts = constant
»Isothermal calorimetry
Ice calorimeter (Bunsen)
Ts = Tc = constant
»Adiabatic calorimetry
Variation in heat input (to the calorimeter)
Ts = Tc ≠ constant
»Heat flowTian-Calvet,
Ts - Tc = constant
7
Isothermal calorimeter
In 1782-84 Lavoisier and the young
mathematician Pierre Simon de
Laplace developed the device to
measure the content of the "element"
caloric in a sample of combustible
oil.
•Ts=Tc=constant
• No temperature rise, temperature not measured
•Heat evolved melts solid
•Measure amount of liquid produced
•Calculated heat evolved from Heat of fusion
8
Isoperibol calorimeter
Surroundings are held at constant temperature Ts=const
Tc is changing as a function of time
There is a heat exchange between surroundings and calorimetric
vessel during the experiment
Witting &Huber (1956)
9
O Kubaschewski, 1955
(NPL, Teddington UK)
•Samples are heated up to the Tr.
•Start of the reaction is indicated by a change in electrical resistance.
•Reaction increases the temperature.=> raise of alumina block temperature
•For calibration electrical energy was out into the furnace. H=Hstart react+Hr
10
Adiabatic calorimeter
• Ts=Tc≠const
No heat losses to the surrounding
• Measure the heat input to
raise sample over a
prescribed temperature
range
11
Adiabatic calorimeter
(Direct reaction calorimetry)
•
•
•
•
Determination of enthalpies of formation
Sample heated from “safe” temperature to
“final” temperature
Safe= Tmax, where no alloying take place
Final=Tmin where complete alloying take
place within 30 min
12
Heat-flow calorimeters
University of Provence in Marseille
Prof. Albert Tian
Invented the heat flux
microcalorimeter: isoperibol with a
thrmopile of 42 junctions
Prof Edouard Calvet
Introduced the differential setup (1948) and a
rational construction of the two twinned
calorimetric elements, transforming Tian's
appliance into a true laboratory instrument
13
Tian-Calvet calorimeters
•
•
Reaction vessel connected to surroundings by a
series of thermocouple junctions
Thermopile
Heat flow between reaction vessel and
surroundings realised as an emf
Seebeck effect
ε=dE/dT
ε=thermoelectric power
E=emf
For n thermocouples E=nε(TA-TC)
Proportion of the flux conducted by
a single thermocouple wire


C
(T
T
)
1
A
C
Total emf in relation to the heat flux
E

C

Twin microcalorimeter
•Micro refers to small heat effects, not small
instruments!
•3D thermopile detector surrounding sample, with
thermocouples providing main path of heat transfer
from calorimeter chamber to block
•Usually twinned construction, but not necessary
(though improves baseline stability) and not an issue
of sample and reference chambers, both used for
experiments
•Measure heat flow from sample chamber to constant
T heat sink, integrate to get heat effect, use an
experimental calibration
Prof. Kleppa calorimeter
15
Inner temperature
Outer temperature
Metal 1
Metal 2
Assembling thermopiles
Thermopiles
Manual: A/Alexsys1000UCDAVIS-1A.pdf, p. 12
Brochure: ALEXSYS-Calorimeter.pdf, p.2
High temperature Heat-Flow calorimeters
Cacciamani - Genova
Setaram HT 1500
Kleppa calorimeter
Taken from presentation of
Prof. P.Nash, Illinois Institute of
Technology
19
Drop calorimetry
• Sample is dropped into the calorimeter
From T1 (Typically room temperature)
To T2 (The calorimeter temperature)
Electrical output from thermopile
H(T2 )-H(T1)
H(T2 )-H(T1)+ΔrH
20
Enthalpy of formation by direct Reaction Drop
Calorimetry
First drop (reaction drop)
Q1  H(cru,TcTr)
 xH( A,TcTr)
 yH(B,TcTr)
 zH(C,TcTr)
  f H( Ax ByCz ,Tc)
Second drop (reference drop)
Q


H
(
cru
,
Tc

Tr
)


H
(
A
B
C
,
Tc

Tr
)
2
x
y
z

(
A
B
C
,
T
)

Q

Q
fH
x
y
z
r
1
2
21
Solution and drop solution calorimetry
• Near room temperature
– Water, aqueous acid of base
– Hydrofluoric acid
– Organic solvents
• At high temperature
– Molten metals, e.g. Sn
– Molten salts, e.g. nitrate or chloride eutectics
– Molten oxides
22
Enthalpy of Formation by metal dissolution Drop Calorimetry
Convert material chemically to a state with
known enthalpy or to common state for
reactants and products, usually a solution
•Samples are dissolved in an appropriate solvent
•Moles solvent >>moles solute
•Samples of the component elements
•Samples of the compound interest
23
Enthalpy of Formation by oxide melt drop solution calorimetry
A => solution ΔH1
B => same solution Δ H2
A => B Δ H3= Δ H1 - Δ H2
The task is to find a reaction scheme and
solvent that lets you do this accurately
•A can be elements, B compound
•A can be binary oxides, B ternary
compound
•A can be end-members, B solid solution or
alloy
•A,B can be different polymorphs
24
Enthalpy of mixing by Metal Dissolution Drop
Calorimetry
Small solute samples are added incrementally to liquid solvent
25
Looks simple but why is it so hard?
Factors effecting the
baseline
Good calorimetry needs
good samples
•Electrical and electronic stability
•Constancy of surroundings
•Mechanical stability of setups
•Chemical issues
– Corrosion
– Vaporization
– Side reactions
•Single phase or pure elements
•Homogeneous
•Chemically analyzed
•Oxidation state known for initial samples
and after dissolution
•No parasitic side reactions
26
Calorimetry
 In the laboratory………and beyond!
Speaker is very grateful to following people for
providing materials for this presentation
•
•
•
•
Prof. Alexandra Navrotsky
Dr. Kristina Lilova
Prof. Philip Nash
Gary Etherington and Pierre Leparlouer
29
TASK
Provided:
Room temperature during calibration and experiment
Temperature of the Calorimeter during calibration and experiment
Ma for Pt, Al,O
Heat capacity equation for Al2O3
Task:
Enthalpy increment of Pt