Unit 1: Section 6 - Thermodynamics Flashcards
What is enthalpy change?
The heat energy transferred in a reaction at constant pressure
What is enthalpy change of formation?
ΔfH - the enthalpy change when 1 mole of a substance is formed from its constituent elements with all substances in their standard states - exothermic for most substances
2Na(s) + 1/2O2(g) -> Na2O(s)
What is enthalpy of combustion?
ΔcH - When 1 mole of a substance undergoes complete combustion in oxygen with all substances in their standard states - exothermic
H2 (g) + 1/2O2(g) -> H2O(l)
What is enthalpy of neutralisation?
ΔneutH - when 1 mole of water is formed in a reaction betweeen an acid and alkali under standard conditions - exothermic
1/2H2SO4(aq) + NaOH(aq) -> 1/2Na2SO4(aq) + H2O(l)
What is ionisation enthalpy?
ΔieH
1st ionisation enthalpy - enthalpy change whe each atom in 1 mole of gaseous atoms loses 1 electron to form 1 mole of gaseous 1+ ions - endothermic
Mg(g) -> Mg+(g) +e-
2nd ionisation enthalpy - enthalpy change when each ion in 1 mole of gasous 1+ ions loses 1 electron to form 1 mole of gaseous 2+ ions - endothermic
Mg+(g) -> Mg2+ +(g) +e-
What is electron affinity?
ΔeaH
1st electron affinity - enthalpy change when each atom in 1 mole of gaseous atoms gains 1 electron to form 1 mole of gaseous 1- ions - exothermic for many non-metals
O(g) + e- -> O-(g)
2nd electron affinity - enthalpy change when each ion in 1 mole of gasous 1- ions gains 1 electron to form 1 mole of gasoues 2- ions - endothermic
O-(g) + e- -> O2-(g)
What is enthalpy of atomisation?
ΔatH - when 1 mole of gaseous atoms is produced from an element in its standard state - endothermic
1/2I2(s) -> I(g)
What is Hydration enthalpy?
ΔhydH
When 1 mole of gaseous atoms dissolve in water (become hydrated) - exothermic
Mg2+(g) + aq -> Mg2+(aq)
What is enthalpy of solution?
ΔsolH
When 1 mole of an ionic solid disolves in an amount of water large enough so that the dissolved ions are well separated and don’t interact with each other - varies
MgCl2(s) + aq -> Mg2+(aq) + 2Cl-(aq)
What is bond dissociation enthalpy?
ΔdisH
When 1 mole of covalent bonds is broken in the gaseous state - endothermic
I2(g) -> 2I (g)
What is lattice enthalpy of formation?
ΔLEFH
When 1 mole of a solid ionic compound is formed from its consistuent ions in the gas phase - exothermic
Mg2+(g) + 2Cl-(g) -> MgCl2(s)
What is lattice enthalpy of dissociation?
When 1 mole of a solid ionic compound is broken up into its constituent ions in the gas phase - endothermic
MgCl2(s) -> Mg2+(g) + 2Cl-(g)
What is enthalpy of vaporisation?
ΔvapH
Whe 1 mole of a liquid is turned into a gas - endothermic
H2O(l) -> H2O(g)
What is enthalpy of fusion?
ΔfusH
When 1 mole of a solid is turned into a liquid - endothermic
Mg(s) -> Mg(l)
What are Born-Haber cycles used for?
Used to calculate lattice enthalpies