Ch5. Energetics
Go to Definitions
Go to Handouts
Go to Presentations
Go to Simulations
Go to Videos
Go to Podcasts
Go to Links
Average bond enthalpy: The average enthalpy change of breaking one mole of a bond in a gaseous atom into its constituent gaseous atoms.
Born-Haber cycle: Energy cycles for the formation of ionic compounds. If there is little agreement between the theoretical and experimental values, this could indicate a degree of covalent character.
Electron affinity: Enthalpy change when an electron is added to an isolated atom in the gaseous state.
Endothermic: A reaction in which energy is absorbed. ΔH is +. Reactants more stable than products.
Enthalpy: The internal energy stored in the reactants. Only changes in enthalpy can be measured.
Entropy: A measure of the disorder of a system. Things causing entropy to increase: 1) increase of number of moles of gaseous molecules; 2) change of state from solid to liquid or liquid to gas; 3) increase of temperature
Exothermic: A reaction in which energy is evolved. ΔH is –. Products more stable than reactants.
Gibb’s free energy: Must be negative for reaction to be spontaneous. ΔG = ΔH – TΔS
Hess’ law: Enthalpy change for a reaction depends only on difference between enthalpy of products and enthalpy of reactants. It is independent of pathway.
Lattice enthalpy: The endothermic process of converting a crystalline solid into its gaseous ions, or the reverse exothermic process. The lattice enthalpy increases with decreasing size of the ions and increasing charge.
Spontaneous: A reaction that has a natural tendency to occur.
Standard conditions: 298 K and 1 atm.
Temperature: A measure of the average kinetic energy.
Standard enthalpy of vaporisation: The energy required to vaporise one mole of a liquid.
Enthalpy of atomisation: The energy required to produce one mole of gaseous atoms from an element in its standard state.
Bond dissociation enthalpy: The energy change when one mole of a specific bond is broken or created under standard conditions.
Enthalpy of Combustion: The energy released when one mole of a compound is burned in excess oxygen.
Standard enthalpy of formation: The energy change when one mole of a compound is formed under standard conditions from its constituent elements in their standard states.
Standard enthalpy of solution: The energy change when one mole of a substance is dissolved in an infinite amount of water under standard conditions.
