Enthalpy & Entropy Definitions
- Created by: annaeb
- Created on: 09-05-21 21:07
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- Entropy & Enthalpy Definitions
- enthalpy change of reaction
- enthalpy change when a reaction occurs in the molar quantities shown in the equation, under standard conditions
- enthalpy change of formation
- enthalpy change when 1 mole of a compound is formed from its constituent elements, under standard conditions
- enthalpy change of combustion
- enthalpy change when 1 mole of a substance completely reacts with oxygen, under standard conditions
- enthalpy change of neutralisation
- the enthalpy change when 1 mole of water is formed from an acid & alkali, under standard conditions
- enthalpy of atomistation
- energy change when 1 mole of gaseous atoms is formed from its elements, under standard coonditions
- e.g.1/2Cl2 (g) -> Cl (g)
- always endothermic- bonds must be broken
- enthalpy of 1st Ionization energy
- energy change when outermost e- is removed from from every atom in 1 mole of gaseous atoms
- endothermic- electron being lost has to overcome attraction from the nucleus in order to leave the atom
- e.g Na (g) -> Na+ (g) + e-
- enthalpy of 2nd ionization energy
- endothermic- electron being lost has to overcome attraction from the nucleus in order to leave the atom
- Ca+ (g) -> Ca2+ (g) +e-
- 1 mole of gaseous 2+ ions are formed from 1 mole of gaseous 1+ ions
- lattice enthalpy
- enthalpy change when 1 mole of an ionic compound is formed from its gaseous ions
- large exothermic value- high energy gasous ions react to form a more stable/ lower energy ionic compound
- Na+ (g)+Cl-(g) ->NaCl (s)
- 1st Electron Affinity
- energy change when every atom in 1 mole of gaseous atoms gains an e-
- exothermic- e- is attracted into the outer shell of the atom by the positive nucleus
- F(g) + e- -> F- (g)
- 2nd Electron Affinity
- O-(g)+ e- ->O2- (g)
- endothermic- e- is repelled by the 1- ion; this repulsion has to be overcome
- 1 mole of gaseous 2- ions is formed from gaseous 1- ions
- enthalpy change of solution
- when 1 mole of a compound is dissolved in water, under standard conditions
- exo/ endothermic
- enthalpy change of hydration
- when 1 mole of aqueous ions are formed from their gaseous ions, under standard conditions
- always exothermic -attraction between ions & water molecules
- Na+ (g) + aq -> Na+ (aq)
- NaCl(s) +aq ->Na + (aq) + Cl- (aq)
- enthalpy change of reaction
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