Thermodynamics

Question 1

what is enthalpy change

Answer 1

is the heat energy transfer in a reaction at constant pressure

Question 2

exothermic

Answer 2

energy out to the surrounding , neg

Question 3

endothermic

Answer 3

eng form the surrounding, positive
breaking bond

Question 4

lattic enthalphy change

Answer 4

measure of the strength of the ionic bond
- eng required to break bond = eng out when bond formed

lattice enthalphy = diff depending on the ions involved

Question 5

lattice enthalphy of formation

Answer 5

enthalp change when a 1 mole of solid ionic compound is formed from it’s gaseous ion

Question 6

lattice entha of dissociation

Answer 6

entha change when one mole of solid ionic compounds completely dissociates into it’s gaseous atom

Question 7

measurement of lattice entha

Answer 7

• no direct way
  1.entha of formation
  2.entha of atomisation ( gaseou satoms form from the elements)
  3. entha of ionisation ( when an atom lose electrons)
  4. entha of electron affinity ( when atom gains electron )

5. lattice entha of formation
   - positive and neg ions form a solid ionic lattice

Question 9

entha change of formation

Answer 9

entna change when 1 mole of compound is formed from it’s elements in their standard states

Question 10

bond dissociation entha

Answer 10

entha changewhen all the bonds of the same type in 1 mole of gaseousmolecule are broken

Question 11

entha change of atomisation

Answer 11

ehtna change when 1 mole of gaseous atoms is formed from an elements in there standard states

Question 12

first ionisation energy

Answer 12

entha change when 1 mole of gaseous 1+ ions is formed from 1 mole of gaseous atoms
O + e- = O-

Question 13

second ionisation energy

Answer 13

entha change when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions
O- + e- = O^2-

Question 14

entha of hydration

Answer 14

entha change when 1 mole of aq ions is formed from gaseous ions

Question 15

entha change of solution

Answer 15

• entha change when 1 mole of ionic substands dissolves in enough solvent to form infinitely dilute solution

Question 16

hess’s law

Answer 16

the total entha change of a reaction is always independent to the route taken

Question 17

purely ionic model

Answer 17

• ions are spherical and charge is distributed evenly

Question 18

theoretical enthalpies

Answer 18

ionic compound usually have some covalent characters
positve or neg ions = not spherical
- positive ions polarise neighbouring neg ions to different extents
- more the polarisation more covalent the bonding will be

Question 19

comparing theoritical and experimental

Answer 19

the experiemental lattice energies are more exothermic than theoretical values
- tells us the bonding is stronger than the calculation
- the difference shows that the ionic bonds ar equite strongly polarised and have more cova cha

Question 20

entrophy

Answer 20

how much disorder there is
- it measures number of ways particles can be arranged
- the number of ways the energy can be shared out between the particles

Question 21

things that affects entrophy

Answer 21

physical state - gas = more entrophy
dissoloution = disolved particles can move more freely
number of particles - more particles , more ways energy can be arranaged

Question 22

calculating entrophy changes

Answer 22

change in s = S product - S reaactant

Question 23

free energy change

Answer 23

is an measure used to predict whether a reaction is feasible
- if more neg or equal to zero = reaction feasible

neg G = doesn’t gaurantee reaction will happen or the rate of reaction

Question 24

effect of temperature to free energy change

Answer 24

• if reaction is exo ( neg ) and has positive entrophy change = change is G always negative ( reaction = feasible )
• if reaction endo ( positive ) and neg entrophy change
  = change G always positive

if change in H is positive and change in S positive then the reaction will only be feasible above certain temp