2. Thermodynamics Definitions Flashcards
A2 thermodynamics definitions
Define Enthalpy of Formation
Enthalpy change when 1 mole of a substance is formed from its constituent elements with all substances in their standard states.
Is Enthalpy of Formation endo or exothermic?
exothermic (-ive) for most substances
Define Enthalpy of Combustion
Enthalpy change when 1 mole of a substance undergoes complete combustion in oxygen with all substances in their standard states
Is Enthalpy of Combustion endo or exothermic?
Exothermic (-ive)
Define Enthalpy of Neutralisation
Enthalpy change when 1 mole of water is formed in a reaction between an acid and alkali under standard conditions
Is enthalpy of neutralisation endo or exothermic?
Exothermic (-ive)
Define first ionisation energy
Enthalpy change when each atom in 1 mole of gaseous atoms loses one electron to form 1 mole of gaseous 1+ ions
Is ionisation energy endo or exothermic?
Endothermic (+ive)
First ionisation energy of Mg?
Mg(g) –> Mg+(g) + e-
Define second ionisation energy
Enthalpy change when each atom in 1 mole of gaseous 1+ ions loses 1 electron to form 1 mole of gaseous 2+ ions
Second ionisation energy of Mg?
Mg+(g) —> Mg2+(g) + e-
Define first electron affinity
Enthalpy change when each atom in 1 mole of gaseous atoms gains 1 electron to form 1 mole of gaseous 1- ions
Is first electron affinity endo or exothermic?
Exothermic (-ive) for many non-metals
First electron affinity of O2?
O(g) + e- —> O-(g)
Define second electron affinity
Enthalpy change when each atom in 1 mole of gaseous 1- ions gains 1 electron to form 1 mole of gaseous 2- ions
Is second electron affinity endo or exothermic?
Endothermic (+ive) as adding -ive electron to -ive ion
Second electron affinity of O2?
O-(g) + e- —> O^2-
Define enthalpy of atomisation
Enthalpy change when 1 mole of gaseous atoms is produced from an element in its standard state
Is enthalpy of atomisation endo or exothermic?
Endothermic (+ive)
Enthalpy of atomisation of iodine?
1/2 I2(s) —-> I(g)
Define hydration enthalpy
Enthalpy change when 1 mole of gaseous ions become hydrated (dissolved in water)
Is hydration enthalpy endo or exothermic?
Exothermic (-ive)
Hydration enthalpy of Mg ions?
Mg^2+(g) + aq —> Mg^2+(aq)
Define enthalpy of solution
Enthalpy change when 1 mole of an ionic solid dissolves in an amount of water large enough so that the dissolved ions are well separated and do not interact with each other
Is enthalpy of solution endo or exothermic?
Varies`
Enthalpy of solution of Magnesium Chloride?
MgCl2(s) + aq —-> Mg^2+(aq) + 2Cl^(aq)
Define bond dissociation enthalpy
Enthalpy change when 1 mole of covalent bonds is broken in the gaseous state
Is bond dissociation enthalpy endo or exothermic?
Endothermic (+ive)
Bond dissociation enthalpy of I-I bond?
I2(g) —> 2I(g)
Define lattice enthalpy of formation
Enthalpy change when 1 mole of a solid ionic compound is formed from its constituent ions in the gas phase
Is lattice enthalpy of formation endo or exothermic?
Exothermic (-ive)
Lattice enthalpy of formation of magnesium chloride?
Mg^2+(g) + 2Cl^-(g) —-> MgCl2(s)
Define lattice enthalpy of dissociation
Enthalpy change when 1 mole of a solid ionic compound is broken up into its constituent ions in the gas phase
Is lattice enthalpy of dissociation endo or exothermic?
Endothermic (+ive)
Lattice enthalpy of dissociation of magnesium chloride?
MgCl2(s) —-> Mg^2+(g) + 2Cl^-(g)
Define enthalpy of vaporisation
Enthalpy change when 1 mole of a liquid is turned into a gas
Is enthalpy of vaporisation endo or exothermic?
Endothermic (+ive)
Enthalpy of vaporisation of water?
H2O(l) —–> H2O(g)
Define enthalpy of fusion
Enthalpy change when 1 mole of a solid is turned into a liquid
Is enthalpy of fusion endo or exothermic?
Endothermic (+ive)
Enthalpy of fusion of Magnesium?
Mg(s) —-> Mg(l)