PHYSICAL - thermodynamics

Question 1

what does hess’s law state?

Answer 1

the enthalpy change for a reaction is independant of the route taken

Question 2

define standard enthalpy of formation?

Answer 2

the enthalpy change when one mole of a compound is formed from its constituent elements in standard conditions, with all products and reactants in their standard states

Question 3

what is the standard enthalpy of an element?

Answer 3

zero, by definition

Question 4

define standard enthalpy of combustion?

Answer 4

the enthalpy change when one mole of a substance is completely burnt in excess oxygen

Question 5

define standard enthalpy of atomisation?

Answer 5

the enthalpy change when one mole of gaseous atoms is formed from a compounds in its standard state and conditions

Question 6

define first ionisation energy?

Answer 6

enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one moles of gaseous 1+ ions.

Question 7

define second ionisation energy?

Answer 7

enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to form one moles of gaseous 2+ ions.

Question 8

define first electron affinity?

Answer 8

enthalpy change where one mole of gaseous atoms gain one mole of electrons to form one mole of gaseous 1- ions

Question 9

define second electron affinity?

Answer 9

enthalpy change where one mole of gaseous 1- ions gain one mole of electrons to form one mole of gaseous 2- ions

Question 10

define lattice enthalpy of formation?

Answer 10

enthalpy change when one mole of solid ionic lattice is formed from its constituent gaseous ions.

Question 11

define lattice enthalpy of dissociation?

Answer 11

enthalpy change when one mole of solid ionic lattice is dissociated into its gaseous ions.

Question 12

define enthalpy of hydration?

Answer 12

enthalpy change when one mole of gaseous ions become hydrated

Question 13

define enthalpy of solution?

Answer 13

enthalpy change when one mole of solute dissolves completely in a solvent to infinite dilution

Question 14

define mean bond dissociation enthalpy?

Answer 14

enthalpy change when one mole of covalent bonds is broken, with all species in the gaseous state.

Question 15

what is born haber cycle?

Answer 15

thermochemical cycle showing all the enthalpy changes, involved in the formation of an ionic compound. start with elements in their standard states.

Question 16

what factors affect the lattice enthalpy of an ionic compound?

Answer 16

size of the ions
charge on the ions

Question 17

how can you increase the lattice enthalpy of a compound? why does this increase?

Answer 17

• smaller ions = charge centres will be closer together so stronger electrostatic forces of attraction between the oppositely charged ions

Question 18

what is the perfect ionic model?

Answer 18

assumes that ions are perfectly spherical and that there is an even charge distribution

Question 19

why is the perfect ionic model innacurate?

Answer 19

polarisation only occurs when small +ive ions are large -ive ions are involved

Question 20

define the terms spontaneous and feasible?

Answer 20

if a reaction is spontaneous and feasible, it will take place of its own accord, does not take account of rate of reaction

Question 21

is a reaction with a positive or negative enthalpy change more likely to be spontaneous?

Answer 21

negative - exothermic