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Guard your heart above all else, for it determines the course of your life.

Alexandra Khvan, Andy Watson

Some like it hot !Or

Calorimetry

• 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?

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• 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

Answer taken from presentation of Prof Alex Navrtosky US Davis

• 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.

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

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But what do we actually measure?

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Calorimeter is an instrument for the measurement of released or absorbed heat during some physical, chemical or biological process

Pierre-Simon LaplacePierre-Simon Laplace Antoine Laurent de LavoisierAntoine Laurent de Lavoisier

1780

Calorimetry

Measure the amount of heat changeMeasure the amount of heat change

Cannot measure enthalpy directly.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 = constant7

Isothermal calorimeter

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•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

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.

Isoperibol calorimeter

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Surroundings are held at constant temperature Ts=constTc is changing as a function of time

There is a heat exchange between surroundings and calorimetric vessel during the experiment

Witting &Huber (1956)

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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

Adiabatic calorimeter

• Ts=Tc≠constNo heat losses to the surrounding

• Measure the heat input to raise sample over a prescribed temperature range

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• 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

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Adiabatic calorimeter(Direct reaction calorimetry)

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University of Provence in Marseille Prof. Albert TianInvented the heat flux microcalorimeter: isoperibol with a thrmopile of 42 junctions

Prof Edouard CalvetIntroduced the differential setup (1948) and a rational construction of the two twinned calorimetric elements, transforming Tian's appliance into a true laboratory instrument 

Heat-flow 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

Tian-Calvet calorimeters

ε=dE/dTε=thermoelectric powerE=emfFor n thermocouples E=nε(TA-TC)

)(1 CA TTC

C

E

Proportion of the flux conducted by a single thermocouple wire

Total emf in relation to the heat flux

Twin microcalorimeter

15Prof. Kleppa calorimeter

•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

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Metal 1Metal 2

Inner temperature

Outer temperature

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Assembling thermopiles

Thermopiles

Manual: A/Alexsys1000UCDAVIS-1A.pdf, p. 12Brochure: ALEXSYS-Calorimeter.pdf, p.2

High temperature Heat-Flow calorimeters

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Setaram HT 1500

Kleppa calorimeterTaken from presentation of Prof. P.Nash, Illinois Institute of Technology

Cacciamani - Genova

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

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Enthalpy of formation by direct Reaction Drop Calorimetry

First drop (reaction drop)

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),(

),(

),(

),(

),(1

TcCBAH

TrTcCHz

TrTcBHy

TrTcAHx

TrTccruHQ

zyxf

Second drop (reference drop)),(),(2 TrTcCBAHTrTccruHQ zyx

21),( QQTCBAH rzyxf

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

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Enthalpy of Formation by metal dissolution Drop Calorimetry

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•Samples are dissolved in an appropriate solvent •Moles solvent >>moles solute•Samples of the component elements•Samples of the compound interest

Convert material chemically to a state with known enthalpy or to common state for reactants and products, usually a solution

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

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Enthalpy of mixing by Metal Dissolution Drop Calorimetry

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Small solute samples are added incrementally to liquid solvent

Looks simple but why is it so hard?

Factors effecting the baseline•Electrical and electronic stability•Constancy of surroundings•Mechanical stability of setups•Chemical issues

– Corrosion– Vaporization– Side reactions

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Good calorimetry needs good samples•Single phase or pure elements•Homogeneous•Chemically analyzed•Oxidation state known for initial samples and after dissolution•No parasitic side reactions

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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

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TASK

Provided:Room temperature during calibration and experimentTemperature of the Calorimeter during calibration and experimentMa for Pt, Al,OHeat capacity equation for Al2O3

Task:Enthalpy increment of Pt