1.4.4

Calorimetry

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Calorimetry

Calorimetry is used to physically measure changes in enthalpy.

Bomb calorimetry

Bomb calorimetry

  • Bomb calorimetry uses a machine called a bomb calorimeter to measure enthalpy changes of combustion.
  • This process involves burning a sample of a compound in a sealed vessel and measuring the temperature change.
    • Often the calorimeter will just determine the temperature change in the vessel and you will have to calculate the enthalpy change of combustion.
Inaccuracy

Inaccuracy

  • Bomb calorimetry can be inaccurate due to:
    • Heat lost to the surroundings.
    • Any incomplete combustion that may take place.
    • Loss of some reactant that evaporates before it combusts.
Calculating enthalpy changes

Calculating enthalpy changes

  • The equation to calculate enthalpy changes from temperature changes is:
    • q = m × c × ΔT
      • q is the heat energy.
      • m is the mass of the sample.
      • c is the specific heat capacity.
      • ΔT is the temperature change.
  • If the pressure is constant, q = ΔcH
Calculating enthalpy changes

Calculating enthalpy changes

  • We have calculated q, the energy given off to the surroundings (the enthalpy change).
    • The units of q are Joules.
  • To determine the enthalpy change of combustion, we must convert Joules into the unit of enthalpy change, Joules per mole.
    • Calculate the number of moles:
      • Moles = mass ÷ Mr
      • ΔH = qmoles\frac{q}{moles}

More Calorimetry

Calorimetry is a very useful technique to determine enthalpy changes.

Different types of calorimetry

Different types of calorimetry

  • Calorimetry can also be used to measure other enthalpy changes.
  • We have considered the combustion reaction that gives off heat.
  • We can also measure any reaction that can be done in a sealed vessel.
    • For example, you can measure the enthalpy change of neutralisation of an acid/base reaction.
    • These reactions take place in a solution that can be inside the vessel.
Accurate temperature changes

Accurate temperature changes

  • You might think that the best measurements to record are the initial and final temperatures of your calorimeter.
  • This is not the case.
    • This is because heat is always being lost from the calorimeter so the final and initial temperatures are inaccurate.
  • Instead, measure the temperature loss after the reaction is complete and extrapolate a line to find the true value.
    • This is shown clearly in the image on the next slide.
Accurate temperature changes

Accurate temperature changes

  • Line extrapolation is shown above.

Example Calculations - Calorimetry Experiment

Below are some example calculations based on the calorimetry experiment.

Combustion of cyclohexane

Combustion of cyclohexane

  • Cyclohexane fuel is burned completely in a calorimeter.
    • There are 200 g of water in the calorimeter.
    • There are 0.5 moles of cyclohexane burnt.
    • The temperature of the water was raised from 298 K to 368 K.
The calculation

The calculation

  • The calculation:
    • q = mcΔT
    • q = 200 g x 4.18 Jg-1K-1 × 70 K
    • q = 58520 Joules
  • Enthalpy change of combustion = q ÷ moles
    • ΔH = −58520 J ÷ 0.5 moles
      • Note the minus sign added. This is because we know the reaction is exothermic since the water's temperature was increased.
    • ΔH = −117040 Jmol-1
    • ΔH = −117.04 kJmol-1
      • Note the final units of kJmol-1 as this is more standard.
Neutralisation reaction

Neutralisation reaction

  • Calculate the heat lost/gained during the reaction between H2SO4(aq) and NaOH(aq):
    • 20 cm3 of the acid is added to an insulate container.
    • 30 cm3 of the base is then added.
    • The temperature change is recorded to be 40 K.
      • Assume the density of the solutions to be the same as water, 1 gcm-3.
      • Assume the specific heat capacity is the same as water's, 4.18 Jg-1K-1.
The calculation

The calculation

  • Because we have assumed that the density is the same as water, we can calculate the mass of the solution as:
    • 1 cm3 = 1 g
    • (20 + 30) cm3 = 50 g
      • The heat change:
    • q = mcΔT
    • q = (50) g x 4.18 Jg-1K-1 x 40 K
    • q = 8360 Joules
    • q = 8.36 kJ
Jump to other topics
1

Physical Chemistry

1.1

Atomic Structure

1.1.1Fundamental Particles1.1.2Isotopes & Mass Number1.1.3Mass Spectrometry1.1.4Electron Shells, Sub-Shells & Orbitals1.1.5Electron Configuration1.1.6Ionisation Energy1.1.7Factors Affecting Ionisation Energies1.1.8Trends of Ionisation1.1.9Specific Impacts on Ionisation Energies1.1.10End of Topic Test - Atomic Structure1.1.11A-A* (AO3/4) - Atomic Structure
1.2

Amount of Substance

1.2.1Relative Masses1.2.2The Mole1.2.3The Ideal Gas Equation1.2.4Empirical & Molecular Formulae1.2.5Balanced Equations1.2.6Percentage Yield1.2.7A-A* (AO3/4) - Percentage Yield1.2.8Atom Economy1.2.9End of Topic Test - Amount of Substance1.2.10A-A* (AO3/4) - Substances & Yield1.2.11Diagnostic Misconceptions - Moles
1.3

Bonding

1.3.1Ionic Bonding1.3.2Covalent & Dative Bonding1.3.3Carbon Structures1.3.4Metallic Bonding1.3.5Physical Properties1.3.6Shapes of Molecules1.3.7Polarity1.3.8Intermolecular Forces1.3.9Intermolecular Forces 21.3.10End of Topic Test - Bonding1.3.11Exam-Style Question - Shape of Molecules1.3.12A-A* (AO3/4) - Bonding1.3.13Diagnostic Misconceptions - Ions1.3.14Diagnostic Misconceptions - Ionic & Covalent1.3.15Diagnostic Misconceptions - Phase Change1.3.16Diagnostic Misconceptions - Boiling1.3.17Diagnostic Misconceptions - Polar Bonds
1.4

Energetics

1.4.1Enthalpy Changes1.4.2Bond Breaking and Making1.4.3Enthalpy Changes: Standard Conditions1.4.4Calorimetry1.4.5Hess' Law1.4.6Bond Enthalpies1.4.7End of Topic Test - Energetics1.4.8Diagnostic Misconceptions - Calorimetry
1.5

Kinetics

1.5.1Collision Theory1.5.2Maxwell-Boltzmann Distribution1.5.3Increasing Rates1.5.4End of Topic Test - Kinetics
1.6

Equilibria

1.6.1Le Chatelier1.6.2Equilibrium Constants1.6.3A-A* (AO3/4) - Energetics, Kinetics, Equilibria1.6.4End of Topic Test - Equilibria1.6.5Diagnostic Misconceptions - Solids
1.7

Redox

1.7.1Redox1.7.2End of Topic Test - Redox
2

Physical Chemistry 2 (A2 Only)

2.1

Thermodynamics (A2 Only)

2.1.1Born-Haber Cycles (A2 Only)2.1.2Born-Haber Cycle Calculations (A2 Only)2.1.3Entropy (A2 Only)2.1.4Free Energy (A2 Only)2.1.5End of Topic Test - Thermodynamics2.1.6A-A* (AO3/4) - Thermodynamics
2.2

Rate Equations (A2 Only)

2.2.1Rate Equations (A2 Only)2.2.2Rate Equations 2 (A2 Only)2.2.3The Arrhenius Equation (A2 Only)2.2.4Experimental Methods for Rates (A2 Only)2.2.5End of Topic Test - Rate Equations2.2.6Exam-Style Question - Rates2.2.7A-A* (AO3/4) - Rate Equations
2.3

The Equilibrium Constant Kp (A2 Only)

2.3.1Properties of Kp (A2 Only)
2.4

Electrochemical Cells (A2 Only)

2.4.1Electrochemical Cells (A2 Only)2.4.2Electrochemical Series (A2 Only)2.4.3Commercial Application (A2 Only)2.4.4End of Topic Test - Kp & Electrochemistry2.4.5A-A* (AO3/4) - Electrochemical Cells2.4.6Diagnostic Misconceptions - Salt Bridges2.4.7Diagnostic Misconceptions - Electrode, Electrolyte
2.5

Acids & Bases (A2 Only)

2.5.1Brønsted-Lowry Acids & Bases (A2 Only)2.5.2pH (A2 Only)2.5.3The Ionic Product of Water (A2 Only)2.5.4Weak Acids & Bases (A2 Only)2.5.5pH Curves & Titrations (A2 Only)2.5.6pH Curves & Titrations 2 (A2 Only)2.5.7Buffer Solutions (A2 Only)2.5.8End of Topic Test - Acids & Bases2.5.9Exam-Style Question - Weak Acids2.5.10A-A* (AO3/4) - Acids & Bases2.5.11Diagnostic Misconceptions - Ammonia is an Alkali2.5.12Diagnostic Misconceptions - Water's Neutrality2.5.13Diagnostic Misconceptions - Concentrate & Strength
3

Inorganic Chemistry

3.1

Periodicity & Trends

3.1.1The Periodic Table3.1.2Trends in the Periodic Table3.1.3End of Topic Test - Periodicity & Trends3.1.4Diagnostic Misconceptions - Atomic Radius
3.2

Group 2

3.2.1Group 2 Chemistry3.2.2End of Topic Test - Group 2
3.3

Group 7

3.3.1Introduction to Halogens3.3.2Reactions of Halogens3.3.3Chlorine & Chlorate(I)3.3.4End of Topic Test - Group 73.3.5Exam-Style Question - Group 73.3.6A-A* (AO3/4) - Periodicity, Group 2 & 7
4

Inorganic Chemistry 2 (A2 Only)

4.1

Period 3 (A2 Only)

4.1.1Period 3 Elements & Oxides (A2 Only)4.1.2Period 3 Oxides (A2 Only)4.1.3End of Topic Test - Period 3
4.2

Transition Metals (A2 Only)

4.2.1General Properties (A2 Only)4.2.2Substitution Reactions (A2 Only)4.2.3Shapes of Complex Ions (A2 Only)4.2.4Colours of Ions (A2 Only)4.2.5Variable Oxidation States (A2 Only)4.2.6Titrations (A2 Only)4.2.7Homogeneous Catalysts (A2 Only)4.2.8Heterogeneous Catalysts (A2 Only)4.2.9End of Topic Test - Transition Metals4.2.10A-A* (AO3/4) - Transition Metals
4.3

Reactions of Ions in Aqueous Solutions (A2 Only)

4.3.1Acidity (A2 Only)4.3.2Identification (A2 Only)4.3.3End of Topic Test - Reactions of Ions in Solution
5

Organic Chemistry 1

5.1

Introduction

5.1.1Naming Conventions5.1.2Mechanism5.1.3Isomerism5.1.4End of Topic Test - Introduction to Organic Chem
5.2

Alkanes

5.2.1Fractional Distillation5.2.2Cracking5.2.3Combustion5.2.4Chlorination5.2.5End of Topic Test - Alkanes
5.3

Halogenoalkanes

5.3.1Substitution Reactions5.3.2Elimination Reactions5.3.3Ozone Depletion5.3.4End of Topic Test - Halogenoalkanes
5.4

Alkenes

5.4.1Introduction to Alkenes5.4.2Reactions of Alkenes5.4.3Polymerisation Reactions5.4.4Properties of Polymers5.4.5End of Topic Test - Alkenes
5.5

Alcohols

5.5.1Production of Alcohols5.5.2Oxidation of Alcohols5.5.3Oxidation of Alcohols - 25.5.4Elimination Reactions5.5.5End of Topic Test - Alcohols5.5.6Exam-Style Question - Alcohols
5.6

Organic Analysis

5.6.1Reactions5.6.2Reactions 25.6.3Mass Spectrometry5.6.4Infrared Spectroscopy5.6.5End of Topic Test - Organic Analysis
5.7

A-A* (AO3/4) - Organic 1

5.7.1A-A* (AO3/4) - Organic 1
6

Organic Chemistry 2 (A2 Only)

6.1

Optical Isomerism (A2 Only)

6.1.1Optical Isomerism (A2 Only)6.1.2End of Topic Test - Optical Isomerism
6.2

Aldehydes & Ketones (A2 Only)

6.2.1Aldehydes & Ketones (A2 Only)6.2.2End of Topic Test - Aldehydes & Ketones
6.3

Carboxylic Acids & Esters (A2 Only)

6.3.1Acids & Esters (A2 Only)6.3.2Acylation (A2 Only)6.3.3End of Topic Test - Carboxylic Acids & Esters
6.4

Aromatic Chemistry (A2 Only)

6.4.1Structure & Reactivity (A2 Only)6.4.2Reactions of Benzene (A2 Only)6.4.3End of Topic Test - Aromatic Chemistry
6.5

Amines (A2 Only)

6.5.1Nature & Preparation of Amines (A2 Only)6.5.2Basicity & Nucleophilicity (A2 Only)6.5.3End of Topic Test - Amines
6.6

Polymers (A2 Only)

6.6.1Condensation Polymers (A2 Only)6.6.2Biodegradability (A2 Only)
6.7

Biological Organic (A2 Only)

6.7.1Amino Acids (A2 Only)6.7.2Proteins (A2 Only)6.7.3DNA (A2 Only)6.7.4Anti-Cancer Drugs (A2 Only)6.7.5End of Topic Test - Biological Organic
6.8

Organic Synthesis (A2 Only)

6.8.1Organic Synthesis (A2 Only)6.8.2Examples of Synthetic Routes (A2 Only)6.8.3End of Topic Test - Polymers & Organic Synthesis
6.9

NMR Spectroscopy (A2 Only)

6.9.1Understanding NMR (A2 Only)6.9.2Carbon-13 NMR (A2 Only)6.9.3Hydrogen-1 NMR (A2 Only)6.9.4Hydrogen-1 NMR 2 (A2 Only)6.9.5End of Topic Test - NMR
6.10

Chromatography (A2 Only)

6.10.1Overview of Chromatography (A2 Only)6.10.2Thin-Layer Chromatography (A2 Only)6.10.3Column Chromatography (A2 Only)6.10.4Gas Chromatography (A2 Only)6.10.5End of Topic Test - Chromatography
6.11

A-A* (AO3/4) - Organic 2

6.11.1A-A* (AO3/4) - Organic 2

Practice questions on Calorimetry

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    Which of the following does bomb calorimetry measure?Multiple choice
  2. 2
    Sources errors in calorimetry:Fill in the list
  3. 3
    Why are the initial and final temperatures in a calorimeter inaccurate?Multiple choice
  4. 4
    We can only convert the mass of a solution to a volume if we know which of the following?Multiple choice
  5. 5
    Two things that change if calculating temperature changes in reaction mixtures:Fill in the list
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Enthalpy Changes: Standard Conditions

Hess' Law