Calorimetry

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Calorimetry

Calorimetry is used to physically measure changes in enthalpy.

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

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

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 = Δ_cH

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 ÷ M_r
  - ΔH = $\frac{q}{moles}$

More Calorimetry

Calorimetry is a very useful technique to determine enthalpy changes.

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

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

Line extrapolation is shown above.

Example Calculations - Calorimetry Experiment

Below are some example calculations based on the calorimetry experiment.

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:
- 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

Calculate the heat lost/gained during the reaction between H₂SO_4(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

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

1Physical Chemistry

1.1Atoms, Molecules & Stoichiometry

1.1.1Relative Masses

1.1.2The Mole

1.1.3Mass Spectrometry

1.1.4Empirical & Molecular Formulae

1.1.5Balanced Equations

1.1.6Molar Volume

1.1.7End of Topic Test - Amount of Substance

1.2Atomic Structure

1.2.1Fundamental Particles

1.2.2Isotopes & Mass Number

1.2.3Electron Shells, Sub-Shells & Orbitals

1.2.4Electron Configuration

1.2.5Ionisation Energy

1.2.6Factors Affecting Ionisation Energies

1.2.7Trends of Ionisation

1.2.8Specific Impacts on Ionisation Energies

1.2.9Electron Affinity

1.2.10End of Topic Test - Atomic Structure

1.2.11A-A* (AO2/3) - Atomic Structure

1.3Chemical Bonding

1.3.1Ionic Bonding

1.3.2Covalent & Dative Bonding

1.3.3Shapes of Molecules

1.3.4Intermolecular Forces

1.3.5Intermolecular Forces 2

1.3.6Electronegativity

1.3.7Bond Length, Bond Energy, & Bond Polarity

1.3.8Metallic Bonding

1.3.9Physical Properties

1.3.10End of Topic Test - Bonding

1.3.11A-A* (AO2/3) - Bonding

1.4States of Matter

1.4.1Simple Covalent Molecules

1.4.2The Ideal Gas Equation

1.4.3States of Matter

1.4.4Particle Diagrams

1.4.5The Liquid State

1.4.6Giant Ionic Lattices

1.4.7Giant Metallic Lattices

1.4.8Giant Covalent Structures

1.4.9Graphene & Fullerene

1.4.10Recycling

1.5Chemical Energetics

1.5.1Calorimetry

1.5.2Bond Enthalpies

1.5.3Enthalpy Changes

1.5.4Hess' Law

1.5.5Born-Haber Cycles

1.5.6Born-Haber Cycle Calculations

1.5.7Entropy

1.5.8Free Energy

1.5.9End of Topic Test - Energetics

1.6Electrochemistry

1.6.1Electrochemical Cells

1.6.2Electrochemical Series

1.6.3Commercial Application

1.6.4Nernst Equation

1.6.5Redox

1.7Equilibria

1.7.1Dynamic Equilibrium & Le Chatelier

1.7.2Kc

1.7.3Kp

1.7.4pH

1.7.5The Ionic Product of Water

1.7.6Weak Acids & Bases

1.7.7Introduction to Solubility Equilibria

1.7.8Solubility Equilibria Calculations

1.7.9Free Energy of Dissolution

1.7.10pH and Solubility

1.7.11Common-Ion Effect

1.7.12End of Topic Test - Kp & Electrochemistry

1.7.13A-A* (AO2/3) - Electrochemical Cells

1.8Partition Coefficient

1.8.1Kpc

1.9Reaction Kinetics

1.9.1Collision Theory

1.9.2Orders, Rate Constants & Equations

1.9.3Rate Graphs

1.9.4Rate Determining Step

1.9.5Maxwell-Boltzmann Distribution

1.9.6Catalysts

1.9.7Homogeneous Catalysts

1.9.8Heterogeneous Catalysts

1.9.9End of Topic Test - Kinetics

1.9.10End of Topic Test - Rate Equations

1.9.11A-A* (AO2/3) - Rate Equations

2Inorganic Chemistry

2.1The Periodic Table

2.1.1The Periodic Table

2.1.2Trends in the Periodic Table

2.1.3End of Topic Test - Periodicity & Trends

2.1.4Ceramics

2.1.5Period 3 Elements & Oxides

2.1.6Period 3 Oxides

2.1.7End of Topic Test - Period 3

2.2Group 2

2.2.1Group 2 Chemistry

2.3Group 17

2.3.1Introduction to Halogens

2.3.2Reactions of Halogens

2.3.3Chlorine & Chlorate(I)

2.3.4End of Topic Test - Group 17

2.3.5A-A* (AO2/3) - Periodicity, Group 2 & 17

2.4Transition Metals

2.4.1General Properties

2.4.2Titrations

2.4.3Shapes of Complex Ions

2.4.4Variable Oxidation States

2.4.5Ligands

2.4.6Colours of Ions

2.4.7Stereoisomerism of Complex Ions

2.4.8Cisplatin

2.4.9Ligand Substitutions & Kstab

2.4.10End of Topic Test - Transition Metals

2.4.11A-A* (AO2/3) - Transition Metals

2.5Nitrogen & Sulfur

2.5.1Nitrogen & Ammonia

2.5.2Formulated vs Manure Fertilisers

2.5.3Nitrogen Containing Fertilisers

2.5.4Fertilizers & Eutrophication

2.5.5Common Atmospheric Pollutants & Their Properties

2.5.6Catalytic Converters

2.5.7Atmospheric Oxides

3Organic Chemistry & Analysis

3.1Introduction to Organic Chemistry

3.1.1Naming Conventions

3.1.2Mechanism

3.1.3Isomerism

3.1.4End of Topic Test - Introduction to Organic Chem

3.2Hydrocarbons

3.2.1Fractional Distillation

3.2.2Cracking

3.2.3Combustion

3.2.4Chlorination

3.2.5End of Topic Test - Alkanes

3.2.6Introduction to Alkenes

3.2.7Reactions of Alkenes

3.2.8Polymerisation Reactions

3.2.9End of Topic Test - Alkenes

3.2.10Arenes

3.2.11Evidence for Structure of Arenes

3.2.12Reactions of Benzene

3.2.13End of Topic Test -Arenes

3.3Halogen Derivatives

3.3.1Properties of Haloalkanes

3.3.2Substitution Reactions of Haloalkanes

3.3.3Environmental Impacts of Haloalkanes

3.3.4End of Topic Test - Halogenoalkanes

3.4Hydroxy Compounds

3.4.1Types of Alcohol

3.4.2Oxidation 1

3.4.3Oxidation 2

3.4.4Elimination

3.4.5Acids & Esters

3.4.6Acyl Chlorides & Acylation

3.4.7Phenols & Their Reactions

3.4.8End of Topic Test - Alcohols

3.5Carbonyl Compounds

3.5.1Carbonyls

3.5.2Hydrogen Bonding & Carbonyls

3.5.3Aldehydes & Ketones

3.5.4Tri-Iodomethane Reaction

3.5.5End of Topic Test -Carbonyls

3.6Carboxylic Acids & Derivatives

3.6.1Properties of Carboxylic Acids

3.6.2Esters

3.6.3Acyl Chlorides

3.6.4End of Topic Test - Carboxylic Acids

3.7Nitrogen Compounds

3.7.1Nature & Preparation of Amines

3.7.2Basicity & Nucleophilicity

3.7.3Amides

3.7.4Reactions of Amino Acids

3.7.5Amino Acids

3.8Polymerisation

3.8.1Properties of Addition Polymers

3.8.2Condensation Polymerisation

3.8.3Effects of Side-Chains on Polymers

3.8.4Hydrolysis of Ester & Amide Groups

3.8.5Proteins

3.8.6DNA

3.8.7Adhesive & Conducting Polymers

3.8.8End of Topic Test - Amines & Proteins

3.9Analytical Techniques

3.9.1Chromatography

3.9.2High-Performance Liquid Chromatography

3.9.3Gas Chromatography

3.9.4IR Spectroscopy

3.9.5Uses of IR Spectroscopy

3.9.6Mass Spectrometry

3.9.7Mass Spectrometry Analysis

3.9.8Nuclear Magnetic Resonance

3.9.9Carbon-13 NMR

3.9.10Proton NMR I

3.9.11Proton NMR II

3.9.12End of Topic Test - Analytical Techniques

3.9.13A-A* (AO2/3) - Analytical Techniques

3.10Organic Synthesis

3.10.1Chirality & Drug Synthesis

3.10.2Organic Synthesis

3.10.3Examples of Synthetic Routes

3.10.4End of Topic Test - Organic Synthesis

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