Enthalpy and entropy

Question 1

what is enthalpy change (ΔH)

Answer 1

heat transferred in a reaction at constant pressure
.measured in KJ mol-1

Question 2

what does ΔH⦵ indicate

Answer 2

.it was measured under standard condition
.298k and 100kPa

Question 3

exothermic and endothermic reactions in enthalpy change

Answer 3

.exothermic reactions are negative

.endothermic reactions are positive

Question 4

what is enthalpy change of formation (ΔH⦵f)

Answer 4

.enthalpy change when 1 mole of a compound is made from its elements in their standard state and conditions

Question 5

what is enthalpy change of atomisation (ΔH⦵at)

Answer 5

enthalpy change when 1 mole of gaseous atoms are formed from the element in its standard state and condition

e.g.
1/2Cl2(g) —> Cl(g)

.always endothermic

Question 6

what is first ionisation energy

Answer 6

.enthalpy change when 1 mole of gaseous 1+ ions are formed from 1 mole of gaseous atoms

Mg+(g) –> Mg+(g) + e-

.always endothermic

Question 7

what is first electron affinity

Answer 7

enthalpy change when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms

O(g) + e- –> O-(g)

Question 8

what is bond enthalpy

Answer 8

enthalpy change when 1 mole of a covalent bond in the gaseous state is broken

Cl2(g) –> 2Cl(g)

.always endothermic

Question 9

what is lattice enthalpy

Answer 9

enthalpy change when one mole of solid ionic compound is formed from its gaseous ions under standard conditions

Na+(g) + Cl-(g) –> NaCl(s)

ΔH⦵latt = 787 kJ mol-1

.always negative/exothermic

.more negative = stronger ionic bonding

Question 10

how does ionic charge effect lattice enthalpy

Answer 10

.ions with higher chargers have stronger electrostatic attractions
.this leads to more energy being released when a lattice is formed = more negative lattice enthalpy

Question 11

how does ionic radius effect lattice enthalpy

Answer 11

.smaller ions have a higher charge density and can pack more close together in a lattice
.this increases electrostatic attraction between ions = more negative lattice enthalpies

Question 12

Born-Haber cycles

Answer 12

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