reactivity 1.2- HL

Question 1

enthalpy change

Answer 1

the heat energy change in a reaction at constant pressure

Question 2

standard enthalpy conditions

Answer 2

298K 100KPa

Question 3

bond dissociation energy

Answer 3

the energy needed to break a particular covalent bond

Question 4

mean bond enthalpy

Answer 4

the average bond dissociation energy for a particular bond in a range of different compounds

Question 5

standard enthalpy of formation of a compound

Answer 5

heat energy change at constant pressure when one mole of a compound is formed from its elements in their standard states under standard conditions

Question 6

standard enthalpy of combustion of an element or a compound

Answer 6

heat energy released at constant pressure when one mole of an element of compound undergoes complete combustion under standard conditions

Question 7

Hess’s law

Answer 7

the total energy change in a reaction is independent of the route

Question 8

born haber cycle

Answer 8

theoretical insight into theroretical energy chabges associated with the formation of ionic solids, provide method of determining value of the lattice enthalpy of an ionic compound

Question 9

first step born haber cycle

Answer 9

metal is converted from a solid to a gas by breaking the metallic bonds holding the atom together (endothermic reaction)
=enthalpy of combustion of your metal

Question 10

second step of born haber cycle

Answer 10

simple covalent gas molecule is converted to atoms by breaking the covalent bond holding atoms together (endothermic)
eg. CL2 -> Cl
=bond enthalpy of your non metal

Question 11

third step of born haber cycle

Answer 11

metal atoms are oxidised into metal ions, they lose electrons
= first ionisation energy of metal (endothermic)
sometimes needs more than one
=second ionisation energy of your metal (endothermic)
eg. Mg 2+

Question 12

fourth step of born haber cycle

Answer 12

non metal atom, gains electrons lost by metal ion
= first ionisation energy of your non metal (endothermic)
sometimes gains more than one
=second ionisation energy of your non metal (exothermic)
non metal atoms are reduced into non metal ions

Question 13

fifth step of born haber cycle

Answer 13

metal and non metal ions combine into a ionic lattic
=lattice enthalpy of your ionic compound

Question 14

enthalpy of formation =

Answer 14

to all the enthalpy energys of the born haber cycle added together

Question 15

how do you represente exo and endothermic changes in born haber cycle

Answer 15

endo= upwards arrow
exo= downward arrow

Question 16

enthalpy of atomistion of a metal

Answer 16

enthapy change when one mole of gaseous metal atoms are formed from the metal element at standard conditions (endothermic)

Question 17

enthalpy of formation of an ionic compound

Answer 17

enthalpy chnage at constant pressure when one mole of an ionic compound is formed from its elements at standard states under standard conditions (exothermic)

Question 18

first electron affinity of non metal

Answer 18

enthalpy change when one mole of gasous non metal atoms gains an electron to form a mole of gasous negative non metal ions (exothermic)

Question 19

enthalpy of atomisation of non metal

Answer 19

enthalpy change when one mole of gasous non metal atoms are formed from the non metal elements in their standard states
(endothermic)

Question 20

lattice enthalpy of ionic compound

Answer 20

enthalpy chnage when one mole of ionic copound is formed from gaseous non metal and metal ions

Question 21

electron affinity

Answer 21

first is always exo
the next to come are always endo

Question 22

what affects lattice enthalpy

Answer 22

size of ions and charge of ions

Question 23

explain how size of ions affect the lattice enthalpy

Answer 23

the smaller the ions the more closely the ions can pack together and attract each other

Question 24

explain how charge of ions affect the lattice enthalpy

Answer 24

the more charged is the ion the stronger the electrostatic force of attraction between them

Question 25

lattice enthalpy is porportional to

Answer 25

(charge on anion) * (charge on cation)/ sum of ionic radii

Question 26

lattice enthalpy definition

Answer 26

the enthalpy change when one mole of solid ionic compound is seperated into its gaseous ions. endothermic, positive enthalpy change

Question 27

why is the first electron affinity usually exothermic

Answer 27

because energy released when the nucleus strongly attracts the first electron is larger than the energy taken in to overcome the inter electronic repulsion

Question 28

why is the second electron affinity usually endothermic

Answer 28

the second electron affinity is endo since the srcond electron is added to a negative ion. Now more energy is needed to overcome the repulsion between the two negatively charged electrons

Question 29

why is the theoretical lattice enthalpy lower than the actual experimental lattice enthalpy

Answer 29

theoretical value assumes ionic model the experimental value is greater due to additional covalent character

Question 30

why is the quantitative value for lattice enthalpy of calcium bromide larger than value for lattice enthalpy of potassium bromide

Answer 30

calcium has smaller ionic raddi and larger charge, meaning the attractive force between the ions is greater resulting in a stronger ionic bond, and increasing the bond lattice enthalpy