energetics

Question 1

enthalpy of combustion

Answer 1

• 1 mole of substance
• combusts completely in excess oxygen
• under standard conditions

Question 2

enthalpy of neutralisation

Answer 2

• 1 mole of water forms
• by neutralisation reaction between acid and alkali
• under standard conditions

Question 3

mean bond enthalpy

Answer 3

energy needed to break 1 mole of a specific type of bond in a gaseous molecule

Question 4

enthalpy of atomisation

Answer 4

1 mole of element in its standard states

is atomised to form 1 mole gaseous atoms

under standard conditions
298k and 100kPa

always ENDOTHERMIC

Na(s)-> Na(g)

Question 5

1st electron affinity

Answer 5

giving 1 mole of electrons to 1 mole of gaseous atoms to form 1 mole of gaseous uninegative ions

EXO

Question 6

lattice energy

Answer 6

gaseous ions form 1 mole of ionic solid
298k and 100kPa
always EXO

2K+(g)+ S2-(g)-> K2S(s)

Question 7

lattice enthalpy

Answer 7

1 mole of solid ionic lattice is formed from its gaseous ions under standard conditions

Question 8

what is the relationship between lattice enthalpy and ionic bonding strength?

Answer 8

greater lattice enthalpy means stronger ionic bonding

e.g NaCl has higher lattice enthalpy then KCl as the Na+ ion is smaller than K+ so stronger ionic charge

Question 9

2nd electron affinity

Answer 9

giving 1 mole of electrons
to 1 mole of gaseous uninegative ions
form 1 mole of gaseous dinegative ions

ENDOTHERMIC- putting together 2 electrons, they repel

Question 10

enthalpy of hydration

Answer 10

1 mole of gaseous ions is dissolved in water

EXO as you form bonds with water

Question 11

enthalpy of solution

Answer 11

1 mole of ionic solid dissolves in water

both EXO and ENDO as you break and form bonds with water

Question 12

despite it’s high lattice enthalpy, NaCl is soluble. what other factors are important in enabling NaCl to be soluble in water?

Answer 12

enthalpy of solution

and

enthalpy of hydration

Question 13

explain why MgO is insoluble in water (2)

Answer 13

ionic attraction too strong cannot be overcome by water
Cant form H bonds with the ions as lattice cant break down

Question 14

explain why energy is needed to break an ionic lattice (2)

Answer 14

must break strong ionic bonds between oppositely charged ions
requires energy

Question 15

why is energy released when ions are hydrated?

Answer 15

hydrogen bonds form between ion and water molecule, forming bonds is exothermic and releases energy

Question 16

define entropy

Answer 16

measure of the dispersal of energy in a system

higher entropy= more disorder (gases)