15 HL Energetics / Thermochemistry Flashcards
What is ionisation energy?
The ionisation energy (ΔHIEꝋ) is the standard enthalpy change that occurs on the removal of 1 mole of electrons from 1 mole of gaseous atoms or positively charged ions
Are ionisation energies exo/endothermic?
Ionisation energy is always endothermic as energy is need to overcome the attraction between an electron and the nucleus
What is the first ionisation energy?
The first ionisation energy (ΔHIE1ꝋ) is the energy required to remove one mole of electrons from 1 mole of gaseous atoms of an element to form 1 mole of 1+ ions in the gaseous phase
Give an equation for the first ionisation energy for aluminium
ΔHIE1ꝋ. Al (g) → Al+ (g) + e– ΔHIE1ꝋ = +577 kJ mol-1
What is the second ionisation energy?
The second ionisation energy (ΔHIE2ꝋ) is the energy required to remove 1 mole of electrons from 1 mole of gaseous 1+ ions to form 1 mole of 2+ ions in the gaseous phase
Give the equation for the second ionisation of aluminium
ΔHIE2ꝋ Al+ (g) → Al2+ (g) + e– ΔHIE2ꝋ = +1820 kJ mol-1
What is the enthalpy of atomisation?
The enthalpy of atomisation (ΔHatꝋ) is the standard enthalpy change that occurs on the formation of 1 mole of separate gaseous atoms an element in its standard state
Is the enthalpy of atomisation always endo/exothermic?
The ΔHatꝋ is always endothermic as energy is always required to break any bonds between the atoms in the element or to break the element into its gaseous atoms
What is the sign for the enthalpy of atomisation?
Since this is always an endothermic process, the enthalpy change will always have a positive value
Give the enthalpy of atomisation for chlorine.
½Cl (g) → Cl (g) ΔHatꝋ = +122 kJ mol -1
Give the enthalpy of atomisation for sodium
Na (s) → Na (g) ΔHatꝋ = +108 kJ mol -1
What is electron affinity?
The electron affinity (ΔHEAꝋ) of an element is the energy change when 1 mole of electrons is gained by 1 mole of gaseous atoms of an element to form 1 mole of gaseous ions under standard conditions
Give the equation for the first enthalpy of atomisation for chlorine?
Cl (g)+ e– → Cl– (g) ΔHEAꝋ = -364 kJ mol-1
Is the first electron affinity always endo/exothermic?
The first electron affinity is always exothermic as energy is released when electrons are attracted to the atoms
Is the SECOND electron affinity always endo/exothermic?
However, the second electron affinity of an element can be endothermic as illustrated by oxygen:
O– (g) + e– → O2- (g) ΔHEAꝋ = +844 kJ mol-1
WHy is the second electron affinity of oxygen endothermic?
This is because a large force of repulsion must be overcome between the negatively charged ion and the second electron requiring a large input of energy
What is the lattice enthalpy?
The lattice enthalpy (ΔHlatꝋ) is defined as the standard enthalpy change that occurs on the formation of 1 mole of gaseous ions from the solid lattice
Is the lattice enthalpy always endo/exothermic?
The ΔHlatꝋ is always endothermic as energy is always required to break any bonds between the ions in the lattice
Therefore what sign does the lattice enthalpy have?
Since this is always an endothermic process, the enthalpy change will always have a positive value
Give the equation for the lattice enthalpy of NaCl?
NaCl (s) → Na+ (g) + Cl- (g) ΔHlatꝋ = +790 kJ mol -1
What is the standard enthalpy change of solution?
The standard enthalpy change of solution (ΔHsolꝋ) is the enthalpy change when 1 mole of an ionic substance dissolves in sufficient water to form an infinitely dilute solution
What is the symbol (aq) used to describe?
The symbol (aq) is used to show that the solid is dissolved in sufficient water
Is enthalpy of solution exo/endothermic?
BOTH
ΔHsolꝋ can be exothermic (negative) or endothermic (positive)
Give the equation for the enthalpy of solution of LiBr
LiBr (s) → LiBr (aq) ΔHsolꝋ = -48.8 kJ mol -1
Give the equation for the enthalpy of solution of KCl
KCl (s) → KCI (aq) ΔHsolꝋ = +17.2 kJ mol -1
What is the standard enthalpy change of hydration?
The standard enthalpy change of hydration (ΔHhydꝋ) is the enthalpy change when 1 mole of a specified gaseous ion dissolves in sufficient water to form an infinitely dilute solution
Give the equation for the enthalpy of hydration of magnesium
Mg2+ (g) → Mg2+ (aq) ΔHhydꝋ = -1963 kJ mol -1
Give the equation for the enthalpy of hydration of bromine
Br- (g) → Br- (aq) ΔHhydꝋ = -328 kJ mol -1
What do hydration enthalpies measure?
Hydration enthalpies are the measure of the energy that is released when there is an attraction formed between the ions and water molecules
Are hydration enthalpies endo/exothermic?
Hydration enthalpies are exothermic
When is the term solvation used for enthalpy of hydration?
The term solvation is used in place of hydration if water has been replaced by another solvent
What is formed when an ionic solid dissolves in water?
When an ionic solid dissolves in water, positive and negative ions are formed
Why do ionic solids dissolve in water?
Water is a polar molecule with a δ- oxygen (O) atom and δ+ hydrogen (H) atoms which will form ion-dipole attractions with the ions present in the solution