Energetics+thermochemistry

back to IB chemistry = Topic notes = = = = Investigations = Prescribed investigations

Other investigations Analysis = Resources =

Hess Law
Below are the answers to all/most questions on the three exercise sheets above

Bond enthalpies
**Standard enthalpy of formation and combustion**

**Born Haber cycles**

Tutorials
[|flow of heat]: this one also helps understanding bonding Like this one because it also links it to bonding and kinetic theory: [|heating curves] Some animations on calorimeters: [|calorimeter1] [|calorimeter2] Calorimetry experiments[|Calorimetry experiment simulations] [|Hess's law calculations] [|Tutorial Hess's law] [|BBC test bite on Hess's law] [|bond enthalpies] [|Entropy] Gibbs free energy from a biology perspective: [|Gibbs free energy in biology] Extension: an animation showing enthalpy changes when an ionic substance dissolves: [|dissolution of ammonium nitrate] [|BBC bitesize enthalpy of solution]

Data sheet
[|Organic compounds thermodynamic data]

** Remember: **

 * Check the unit of an enthalpy change; either it is in kJ or kJ mol-1.
 * When calculating molar enthalpy change do not use the mass of the water/surroundings to calculate the number of moles. Also make sure you clearly state the sign i.e + or -.
 * When calculating free energy you should have enthalpy and entropy in the same units either both in kJ or both in J; temperature should be in K.
 * Make sure the state symbols are (g) in your equations defining ionization energy, electron affinity and bond enthalpy.
 * Bond enthalpy is for 1 mole of covalent bonds in gaseous molecules to form gaseous atoms.
 * Bond enthalpy is also an AVERAGE
 * Calculating enthalpy change using bond enthalpies is **reactants - products** as is using enthalpies of combustion; other are **products - reactants.**