(c) doc bCALORIMETER EXPERIMENTS & CALCULATION of ENERGY TRANSFER

Doc Brown's Chemistry KS4 science GCSE/IGCSE/O level/A Level Chemistry Revision Notes

PART D Exothermic and Endothermic Energy Changes – Chemical Energetics  Methods of determining energy transfers and calculation of energy changes from calorimetric data.

Experimental methods for obtaining vales for energy transfer changes in chemical reactions are described and how to do the calculations based on calorimeter experiment results. Calculation of energy transferred from experimental data is explained. A simple calorimeter is described and how to obtain energy transfer measurements. Revision notes for GCSE/IGCSE/O Level/basic stuff for GCE Advanced Level AS students. These revision notes on calorimeter experiments, procedures and calculations of energy transfers in chemical reactions should prove useful for the new AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science courses.


Sub–index for ENERGY CHANGES: 1. Heat changes in chemical/physical changes – exothermic and endothermic  *  2. Reversible reactions and energy changes  *  3. Activation energy and reaction profiles  *  4. Catalysts and activation energy  *  5. Introduction to bond energy/enthalpy calculations  *  6. Calorimeter methods of determining energy changes and examples of experiments  *  7. Energy transfer calculations from calorimeter results (this page)

See also Advanced A Level Energetics–Thermochemistry – Enthalpies of Reaction, Formation & Combustion

and enthalpy calculations from calorimetry data for Advanced A Levels students



 

6. The experimental determination of energy changes using simple calorimeters

The basic principles of calorimetry

(c) doc b

Using this apparatus you can observe changes in heat energy accompanying the following changes -


(i) salts dissolving in water,

 (ii) neutralisation reactions,

(iii) displacement reactions,

(iv) precipitation reactions


and when these reactions take place in solution, the
temperature changes can be measured to calculate and compare the relative heat energy changes.

This method 7.1 is can be used for any non–combustion reaction that will happen spontaneously at room temperature involving liquids or solid reacting with a liquid.

This method involves using a simple polystyrene cup as the calorimeter container - polystyrene is a poor conductor of heat - good insulator.

For extra insulation you can place the polystyrene container in a larger beaker containing a thick layer of cotton wool wrapped around to minimise heat loss - the main source of error in the experiment. Lastly, a sealing lid to stop convection in air. All these measures help reduce the heat loss and quite accurate results can be obtained even with this simple apparatus.

The reactants are weighed in if solid and/or a known volumes of any liquids involved (usually water or aqueous solution) added.

The mixture could be a salt and water (heat change on dissolving) or an acid or an alkali solution (heat change of neutralisation). It doesn't matter whether the change is exothermic (heat released or given out, temperature increases) or endothermic (heat absorbed or taken in, temperature decreases). See calculations below.

You measure the initial temperature of the reactants at the start and the final maximum/minimum temperature when the reaction is done. You should gently stir the mixture after the initial temperature reading to ensure all reactants react!

Subtracting one from the other gives the temperature change.

If the reaction is exothermic the temperature rises and if the temperature falls its an endothermic change.

From the temperature rise or temperature fall and the heat capacity of the water you can calculate how much heat was released or how much heat energy was absorbed by a specific quantities of chemicals reacting (or even the energy transfer when a salt dissolves in water, which can be exothermic or endothermic).

Energy transferred in J = mass of solution in grams X specific heat capacity of water (4.2J/goC) X temperature change in oC

You can then calculate the amount of energy released/absorbed per gram or per mole.


Whether the reaction is exothermic or endothermic depends on the reactant chemicals involved and the type of reaction. Some types of reaction are always exothermic or always endothermic, other reactions could be either exothermic or endothermic.

Some examples are briefly described below and all can be investigated with the humble polystyrene calorimeter.


(i) Neutralisation: Mixing an acid with an alkali always gives an exothermic reaction - the temperature rises.

e.g. neutralising hydrochloric acid with sodium hydroxide to give sodium chloride and water

HCl(aq)  +  NaOH(aq)  ===>  NaCl(aq)  +  H2O(l)

(ii) Dissolving salts: Adding the salts ammonium nitrate or ammonium chloride to water gives a temperature fall, an endothermic dissolving change.

e.g. dissolving ammonium nitrate in water

 NH4NO3(s)  +  aq  ===> NH4NO3(aq)

Dissolving anhydrous calcium chloride gives a temperature rise - exothermic

(iii) Metal displacement reaction: Adding zinc to copper sulfate produces an exothermic displacement reaction shown by the rise in temperature.

zinc  +  copper(II) sulfate  ===>  zinc sulfate  +  copper

Zn(s)  +  CuSO4(aq)  ===>  ZnSO4(aq)  +  Cu(s)

The more reactive zinc displaces the less reactive copper out of solution.

(c) doc b

You can investigate burning liquid hydrocarbons like hexane - but smokey and inaccurate,

alcohols like ethanol burn more efficiently with a 'cleaner' blue flame

This method 7.2 is specifically for determining the heat energy released (given out) for burning fuels. The burner is weighed before and after combustion to get the mass of liquid fuel burned. The thermometer records the temperature rise of the known mass of water (1g = 1cm3).

The heat from the fuel combustion heats up the water. From the heat capacity of the water and the temperature rise you can calculate how much heat was released by a specific mass of fuel.

You measure the temperature of the reactants at the start and the final maximum/minimum temperature when the reaction is done. Subtracting one from the other gives the temperature change.

Energy transferred in J = mass of water in grams X specific heat capacity of water (4.2J/goC) X temperature change in oC

You can then calculate the amount of energy released per gram or per mole.

You can use this system to compare the heat output from burning various fuels. The bigger the temperature rise, the more heat energy is released. See calculations below for expressing calorific values.

BUT you must conduct the experiments under 'fair test' conditions.

apart from repeating experiments (to eliminate anomalous results), you must use the same burner & wick (if possible), same volume (mass) of water, same calorimeter, burn for the same length of time, same insulation set-up

This is a very inaccurate method because of huge losses of heat e.g. radiation from the flame and calorimeter, conduction through the copper calorimeter, convection from the flame gases passing by the calorimeter etc. BUT, at least using the same burner and set–up, you can do a reasonable comparison of the heat output of different fuels. You can burn simple hydrocarbons like hexane, alcohols like ethanol and even vegetable oils and it is possible to do a crude calibration of the calorimeter using a fuel of known energy output on complete combustion.

You can investigate the temperature rise produced in a known mass of water by the combustion of the series alcohols, methanol, ethanol, propanol, butanol using this simple calorimeter system to get a pattern for a homologous series of organic compounds.

See GCSE/IGCSE/O Level notes on chemistry of alcohols

BOMB CALORIMETER Advanced Level students need to know about the bomb calorimeter for determining enthalpies of combustion as well as the methods described above.

7. Calculations from the experimental calorimeter results

  • PLEASE NOTE that section 7. is for higher GCSE students and an introduction for advanced level students of how to do energy change (enthalpy change) calculations from experimental data.

  • The calculation method described below applies to both experimental methods 6.1 and 6.2 described above.

  • You need to know the following:

    • the mass of material reacting in the calorimeter (or their concentrations and volume),

    • the mass of water in the calorimeter,

    • the temperature change (always a rise for method 6.2 combustion),

    • the specific heat capacity of water, (shorthand is SHCwater), and this is 4.2J/goC (for advanced 4.2J g–1 K–1),

      • this means it means the addition of 4.2 J of heat energy to raise the temperature of 1g of water by 1oC.

  • Example 7.1 typical of calorimeter method 7.1

    • Measuring the energy transfer when a salt dissolves in water

    • 5g of ammonium nitrate (NH4NO3) was dissolved in 50cm3 of water (50g) and the temperature fell from 22oC to 14oC.

    • Temperature change = 22 – 14 = 8oC (endothermic, temperature fall, heat energy absorbed)

    • Heat absorbed by the water = mass of water x SHCwater x temperature

      • = 50 x 4.2 x 8 = 1680 J (for 5g)

      • heat energy absorbed on dissolving = 1680 / 5 = 336 J/g of NH4NO3 

    • this energy change can be also expressed on a molar basis.

      • Relative atomic masses Ar: N = 14, H = 1, O = 16

      • Mr(NH4NO3) = 14 + (1 x 4) + 14 + (3 x 16) = 80, so 1 mole = 80g

      • Heat absorbed by dissolving 1 mole of NH4NO3 = 80 x 336 = 26880 J/mole

      • At A level this will be expressed as enthalpy of solution = ΔHsolution = +26.88 kJ/mol

      • The data book value is +26 kJmol–1

  • Example 7.2 typical of calorimeter method 7.2

    • Determining the energy change for a typical fuel combustion reaction

    • 100 cm3 of water (100g) was measured into the calorimeter.

    • The spirit burner contained the fuel ethanol C2H5OH ('alcohol') and weighed 18.62g at the start.

    • The initial temperature of the water is taken.

    • After burning some time, the flame is extinguished, the water stirred gently and the final water temperature is taken to get the temperature rise.

    • The burner and fuel are then reweighed to see how much fuel had been burned.

    • After burning it weighed 17.14g and the temperature of the water rose from 18 to 89oC.

    • The temperature rise = 89 – 18 = 71oC (exothermic, heat energy given out).

    • Mass of fuel burned = 18.62–17.14 = 1.48g.

    • Heat absorbed by the water = mass of water x SHCwater x temperature

      • = 100 x 4.2 x 71 = 29820 J (for 1.48g)

      • heat energy released per g = energy supplied in J / mass of fuel burned in g

      • heat energy released on burning = 29820 / 1.48 = 20149 J/g of C2H5OH

    • this energy change can be also expressed on a molar basis.

      • Relative atomic masses Ar: C = 12, H = 1, O = 16

      • Mr(C2H5OH) = (2 x 12) + (1 x 5) + 16 + 16 = 46, so 1 mole = 46g

      • Heat released (given out) by 1 mole of C2H5OH = 46 x 20149 = 926854 J/mole or 927 kJ/mol (3 sf)

      • At AS level this will be expressed as the ...

      • Enthalpy of combustion of ethanol = ΔHcombustion (ethanol) = –927 kJmol–1

      • This means 926.9 kJ of heat energy is released on burning 46g of ethanol ('alcohol').

      • The data book value for the heat of combustion of ethanol is –1367 kJmol–1, showing lots of heat loss in the experiment!

      • It is possible to get more accurate values by calibrating the calorimeter with a substance whose energy release on combustion is known.

  • Example 7.3. Determining the energy change of neutralisation of hydrochloric acid and sodium hydroxide

    • You can do this experiment by mixing equal volumes of equimolar concentrations of dilute hydrochloric acid and dilute sodium hydroxide. e.g. 25 cm3 of each in the polystyrene calorimeter as previously described.

    Suppose after mixing, via accurate pipettes, 25.0 cm3 of 1.0 mol dm–3 hydrochloric acid and 25.0 of 1.0 mol dm–3, sodium hydroxide solutions the temperature rise with an accurate thermometer was 7.1oC.

    Calculate the energy of neutralisation for the reaction:

    HCl(aq)  +  NaOH(aq)  ===>  NaCl(aq)  +  H2O(l)

    Calculation   (SHC shorthand for specific heat capacity, 4.18 is more accurate than 4.2)

    Using the SHC for water and the total mass is effectively 50 g (actually ~50 cm3 of NaCl solution).

    heat released (J) = mass x  SHCH2O x temperature change (ΔT, oC)

    =  50 x 4.18 x 7.1 = 1483.9 J, 1.4839 kJ

    From the equation: mol HCl = mol NaOH = 1.0 x 25/1000 = 0.025 mol

    Therefore scaling up to 1 mol gives a numerical enthalpy change of 1.4839 x 1/0.025 = 59.4 kJ (3 s.f.)

    Since the temperature rose indicating an exothermic reaction, the energy of this neutralisation is ..

    Energy of neutralisation for HCl + NaOH = 59.4 kJ mol–1  (only accurate to 3 sf)

     


Further comments


TOP OF PAGE


Sub–index for ENERGY CHANGES: 1. Heat changes in chemical/physical changes – exothermic and endothermic  *  2. Reversible reactions and energy changes  *  3. Activation energy and reaction profiles  *  4. Catalysts and activation energy  *  5. Introduction to bond energy/enthalpy calculations  *  6. Calorimeter methods of determining energy changes  *  7. Energy transfer calculations from calorimeter results

See also Advanced A Level Energetics–Thermochemistry – Enthalpies of Reaction, Formation & Combustion

and enthalpy calculations from calorimetry data for Advanced A Levels students


 


how do you do a simple calorimetry experiment to measure a heat energy change? what apparatus do you need for calorimetry? what is the calorimeter procedure for measuring a heat energy change? Revision notes on simple calorimeter experiments in chemistry calculations KS4 Science GCSE/IGCSE/O level Chemistry Information on simple calorimeter experiments in chemistry calculations for revising for AQA GCSE Science, Edexcel Science chemistry IGCSE Chemistry notes on simple calorimeter experiments in chemistry calculations OCR 21st Century Science, OCR Gateway Science notes on simple calorimeter experiments in chemistry calculations WJEC gcse science chemistry notes on simple calorimeter experiments in chemistry calculations CIE O Level chemistry CIE IGCSE chemistry notes on simple calorimeter experiments in chemistry calculations CCEA/CEA gcse science chemistry (revise courses equal to US grade 8, grade 9 grade 10) science chemistry courses revision guides explanation chemical equations for simple calorimeter experiments in chemistry calculations educational videos on simple calorimeter experiments in chemistry calculations guidebooks for revising simple calorimeter experiments in chemistry calculations textbooks on simple calorimeter experiments in chemistry calculations calorimeter results & calculations for AQA AS chemistry, calorimeter results & calculations for Edexcel A level AS chemistry, calorimeter results & calculations for A level OCR AS chemistry A, calorimeter results & calculations for OCR Salters AS chemistry B, calorimeter results & calculations for AQA A level chemistry, calorimeter results & calculations for A level Edexcel A level chemistry, calorimeter results & calculations for OCR A level chemistry A, calorimeter results & calculations for A level OCR Salters A level chemistry B calorimeter results & calculations for US Honours grade 11 grade 12 calorimeter results & calculations for pre-university chemistry courses pre-university A level revision notes for calorimeter results & calculations  A level guide notes on calorimeter results & calculations for schools colleges academies science course tutors images pictures diagrams for calorimeter results & calculations A level chemistry revision notes on calorimeter results & calculations for revising module topics notes to help on understanding of calorimeter results & calculations university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 11 grade 11 AQA A level chemistry notes on calorimeter results & calculations Edexcel A level chemistry notes on calorimeter results & calculations for OCR A level chemistry notes WJEC A level chemistry notes on calorimeter results & calculations CCEA/CEA A level chemistry notes on calorimeter results & calculations for university entrance examinations gcse chemistry revision free detailed notes on calorimeter results & calculations to help revise igcse chemistry igcse chemistry revision notes on calorimeter results & calculations O level chemistry revision free detailed notes on calorimeter results & calculations to help revise gcse chemistry free detailed notes on calorimeter results & calculations to help revise O level chemistry free online website to help revise calorimeter results & calculations for gcse chemistry  free online website to help revise calorimeter results & calculations for igcse chemistry free online website to help revise O level calorimeter results & calculations chemistry how to succeed in questions on calorimeter results & calculations for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on calorimeter results & calculations to help to pass gcse chemistry questions on calorimeter results & calculations a good website for free help to pass igcse chemistry with revision notes on calorimeter results & calculations a good website for free help to pass O level chemistry GCSE (9–1, 9-5 & 5-1) science courses

KS3 SCIENCE QUIZZES ALPHABETICAL INDEX
GCSE grade 9-1 & IGCSE CHEMISTRY Doc Brown's Travel Pictures & Notes
ADVANCED LEVEL CHEMISTRY [SEARCH BOX] - see below
GCSE 9-1 Physics Revision Notes GCSE 9-1 Biology Revision Notes
All website content © Dr Phil Brown 2000 onwards. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries and references to science course specifications are unofficial. Email doc b: chem55555@hotmail.com

 Doc Brown's Chemistry 

*

 For latest updates see https://twitter.com/docbrownchem

 Have your say about doc b's website

TOP OF PAGE