Doc Brown's A Level Chemistry Advanced Level Theoretical Physical Chemistry - AS A2 Level Revision Notes - Basic Thermodynamics
GCE Thermodynamics-thermochemistry sub-index links below
Part 2 ΔH Enthalpy Changes contd. - Lattice Enthalpy, Born Haber Cycle, Enthalpies of Solution, Enthalpies of Ion Hydration
2.1 continued - The Hess's Law cycle of the energy changes when a solid dissolves in a solvent e.g. water - Calculations involving Enthalpy of hydration of ions, enthalpy of solution, lattice enthalpy
The Hess's Law cycle connecting lattice enthalpy, enthalpies of hydration of ions and the enthalpy of solution is constructed and how to use it in calculations. A discussion of four cases of dissolving/insolubility are discussed with the aid of enthalpy level diagrams using the Hess's Law cycle for dissolving previously described.
Energetics index: GCSE Notes on the basics of chemical energy changes - important to study and know before tackling any of the three Advanced Level Chemistry pages Parts 1-3 here * Part 1a-b ΔH Enthalpy Changes 1.1 Advanced Introduction to enthalpy changes - reaction, formation, combustion : 1.2a & 1.2b(i)-(iii) Thermochemistry - Hess's Law and Enthalpy Calculations - reaction, combustion, formation etc. : 1.2b(iv) Bond Enthalpy Calculations : 1.3a-b Experimental methods for determining enthalpy changes and treatment of results : 1.4 Some enthalpy data patterns : 1.4a The combustion of linear alkanes and linear aliphatic alcohols : 1.4b Some patterns in Bond Enthalpies and Bond Length : 1.4c Enthalpies of Neutralisation : 1.4d Enthalpies of Hydrogenation of unsaturated hydrocarbons and evidence of aromatic ring structure in benzene : Extra Q page A set of practice enthalpy calculations with worked out answers ** Part 2 ΔH Enthalpies of ion hydration, solution, atomisation, lattice energy, electron affinity and the Born-Haber cycle : 2.1a-c What happens when a salt dissolves in water and why? : 2.1d-e Enthalpy cycles involving a salt dissolving : 2.2a-c The Born-Haber Cycle *** Part 3 ΔS Entropy and ΔG Free Energy Changes : 3.1a-g Introduction to Entropy : 3.2 Examples of entropy values and comments * 3.3a ΔS, Entropy and change of state : 3.3b ΔS, Entropy changes and the feasibility of a chemical change : 3.4a-d More on ΔG, Free energy changes, feasibility and applications : 3.5 Calculating Equilibrium Constants : 3.6 Kinetic stability versus thermodynamic feasibility * PLEASE note that delta H/S/G values vary slightly from source to source, so I apologise in advance for any inconsistencies that may arise as I've researched and developed each section.
2.1 continued - The Hess's Law cycle of the energy changes when a solid dissolves
See Part 2.2 for Born-Haber Cycle Calculations
Section 2.1d Examples of 'dissolving' enthalpy cycles using Hess's Law
Example 1 Dissolving the salt sodium chloride
From above the processes (i), (ii) and (iii) put together in a Hess's Law enthalpy cycle for dissolving an ionic compound.
From above the processes (i), (ii) and (iii) are now put together in a Hess's Law cycle for sodium chloride.
Example 2 Dissolving the alkali potassium hydroxide
Example 3 Dissolving the salt aluminium fluoride
Section 2.1e Examples of explaining salt solubility or insolubility
In the case of salts/binary compounds etc. that do not dissolve, the bonding forces are too strong e.g. iron(III) oxide, aluminium oxide etc. where you have two highly charged ions attracting each other. more on this below in which entropy changes are mentioned, but entropy as a concept is dealt with in detail on Part 3 Entropy and Free Energy changes. Four generalised cases are discussed below but using enthalpy level diagrams which are helpful in understanding the situation rather then the enthalpy cycle diagrams, which are better for doing calculations in my opinion. The enthalpy of hydration is the enthalpy of solvation when water is the solvent. Water is a very polar solvent and is one of the best solvents for ionic compounds. In example 4. a non-polar solvent is considered, so the term enthalpy of solvation applies rather than enthalpy of hydration.
See Part 2.2 for Born-Haber Cycle Calculations
A level Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre-university students (equal to US grade 11 and grade 12 and AP Honours/honors level courses) revision aids for revising A level chemistry courses revision guides
Website content copyright © Dr W P Brown 2000-2012 All rights reserved on revision notes, puzzles, quizzes, worksheets, x-words etc. * Copying of website material is not permitted firstname.lastname@example.org