thermodynamics Flashcards
in exothermic reactions are bond broken or made
in exothermic reactions bonds are formed
in endothermic reactions are bonds broken or made
in endothermic reactions bond are broken
what factor does the size of an enthalpy change depend on
- the strength/energy of a bond or force
(stronger bonds /forces produce a larger enthalpy change
define enthalpy change of formation
the enthalpy change when 1 mole of substance is formed from it’s constituent elements in their standard states under standard conditions and pressure
write an equation for the enthalpy change of formation for NaCl
Na (s) + 1/2 Cl2 —-> NaCl (s)
define enthalpy change of lattice formation
the enthalpy change when one mole of an ionic compound is from from it’s component ions in a gaseous state
write an equation for the enthalpy change of lattice formation of NaCl
Na+ + Cl- —-> NaCl (s)
what type of energy change is enthalpy change of lattice formation and why?
exothermic
it is forming an electrostatic attraction (ionic bond)
what are the 2 factors that affect enthalpy change of lattice formation and explain why they affect it?
charge on ion = higher charge = strong electrostatic forces between ions = more exothermic lattice formation enthalpy
size of ion = smaller ionic radius = stronger electrostatic forces between ions = more exothermic lattice formation enthalpy
define enthalpy change of atomisation
the enthalpy change when one mole of gaseous atoms are formed
write the equation for the enthalpy change of atomisation of Na
Na (s) —> Na (g)
write an equation for the enthalpy change of atomisation of Cl
1/2 Cl2 (g) —-> Cl (g)
write an equation for the enthalpy change of atomisation of Br
1/2 Br2 (l) —-> Br (g)
write an equation for the enthalpy change of atomisation of S
1/8 S8 (s) —-> S (g)
what type of energy change is enthalpy change of atomisation and why
endothermic, as breaking bonds of attraction
define 1st ionisation enthalpy
The enthalpy change to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
write an equation for the 1st ionisation enthalpy for Na
Na (g) —-> Na+ (g) + e-
what type of energy change is the 1st ionisation enthalpy change
Endothermic, overcoming electrostatic attraction between nucleus and outer electron
what factors affect the 1st ionisation energy
- nuclear charge
- electron shielding
- size of ion
define bond dissociation enthalpy
the enthalpy change when 1 mole of covalent bonds are gaseous state
write an equation for the bond dissociation enthalpy of Cl
Cl2 (g) —-> 2Cl (g)
define 1st electron affinity
the enthalpy change to add 1 mole of electrons to 1 mole of gaseous atoms to make 1 mole of gaseous ions with a -1 charge
write an equation for the 1st electron affinity of Cl (g)
Cl (g) + e- —–> Cl- (g)
what type of energy change is 1st electron affinity
exothermic as an electrostatic attraction between nucleus and electron is being formed
what factors affect 1st electron affinity
- nuclear charge
- electron shielding
- size of atom
define 2nd electron affinity
the enthalpy change when you add one mole of electrons to one mole of gaseous ions with a charge -1 to make 1 mole of gaseous ions with a -2 charge
write an equation for the second affinity of oxygen
O- (g) + e- —-> O2- (g)
what type energy change is 2nd electron affinity
endothermic, electron is being added to an already negatively charged ion. Repulsion between ion and electron must be overcome.
define enthalpy of solution
the enthalpy change when one mole of an ionic substance is completely dissolved in water to infinite dilution
give the equation for enthalpy of solution of MgCl2
MgCl2 (s) —> Mg2+ (aq) + 2Cl- (aq)
define enthalpy of hydration
the enthalpy change when one mole of gaseous ions is diluted to 1 mole of aqueous ions
give the equation for the enthalpy of hydration for Mg2+ (aq)
Mg2+ (aq) + (aq) —-> Mg2+ (aq)
define lattice dissociation enthalpy
the enthalpy change when one mole of an ionic solid is converted to gaseous ions
give the equation for the lattice dissociation enthalpy of MgCl2 (s)
MgCl2 (s) —-> Mg2+ (g) + 2Cl- (g)
what is the equation used to calculate the value for enthalpy of solution
enthalpy of solution = enthalpy of lattice dissociation + enthalpy of hydration
define enthalpy of hydration
forces between partial charges of delta positive and delta minus on water are attracted to ions
is enthalpy of hydration endothermic or exothermic and why
exothermic as a bond is being formed
what 2 factors affect hydration enthalpy and explain why
size of ion
smaller ion = higher charge density therefore stronger attraction between partial charges on water and ion
= more exothermic hydration enthalpy
charge of ion
greater charge of ion = higher charge density = stronger attraction between partial charges on water and ion = more exothermic hydration enthalpy
define lattice dissociation enthalpy
electrostatic forces between postive and negative ions are overcome
why is lattice dissociation enthalpy endothermic
you are breaking bonds
what 2 factors affect the lattice dissociation enthalpy and explain why
size of ion
smaller ion
= higher charge density = stronger electrostatic forces between oppositely charged ions = more endothermic lattice dissociation enthalpy
greater charge on ion = higher charge density = stronger attraction between oppositely charged ions = more endothermic lattice dissociation enthalpy
what chemical property do ionic compounds with very endothermic lattice dissociation enthalpies tend to have and why
ionic compounds with high lattice dissociation enthalpies tend to be insoluble as a lot of energy is needed to break the ionic lattice (electrostatic forces)
if enthalpy of solution is exothermic then what happens to solubility when temperature increases
enthalpy of solution is exothermic so
solubility decreases as temperature increases
if enthalpy of solution is endothermic then what happens to solubility as temperature increases
enthalpy of solution is endothermic so
solubility increases as temperature increases
