topic 8 and 13 enthalpy changes definitions

Question 1

where is chemical energy stores

Answer 1

in the bonds

Question 2

change in enthalpy

Answer 2

heat change per mole in a reaction measure under sc

Question 3

formation

Answer 3

change in enthalpy when 1 mole of product is formed from its elements in their standard state under sc

Question 4

combustion

Answer 4

change in enthalpy when one mole of substance burns completely in oxygen

Question 5

reaction

Answer 5

enthalpy change when when molar quantities as stated in equation react under sc

Question 6

neutralisation

Answer 6

change in enthalpy when 1 mol of water is produced from an acid plus alkali reaction under sc

Question 7

what might be some errors for enthalphy change of combustion

Answer 7

heat loss to surrounding due to radiation

incomplete combustion

not in sc

Question 8

law of conservation

Answer 8

amount of energy in isolated system stays the same

energy cannot be destroyed or created

it can only be transferred from one store to another

Question 9

difficulty when calculation change in enthalpy

Answer 9

high Ea

slow rate of reaction

side reactions take place

toxic products produced

Question 10

how to measure enthalpy

Answer 10

calorimetry test

mean bond enthalpies

hess cycles

Question 11

bond dissociation

Answer 11

enthalpy change when one mol of covalent bond is broken between two atoms with all species are in gas state

Question 11

bond dissociation

Answer 11

enthalpy change when one mol of covalent bond is broken between two atoms with all species are in gas state

Question 12

whys there varying enthapy change values when comparing using mean bond enthalpy values and true values

Answer 12

bc mean bond enthalpy is the average value of bond dissociation enthalpy of a particular bond over many compounds

Question 13

what is born haber cycle

Answer 13

thermo chemical cycle showing all the enthalpy changes in involved in the formation of ionic compounds with elements starting in standard state

Question 14

what affects lattice energy

Answer 14

size of ion and charge of ion

Question 15

what is perfect ionic model

Answer 15

assumes ions are perfecticly spherical with charge evenl distributed throughout ion

attractions purely electrostatic

Question 16

why are they not perfect

Answer 16

ions are not perfect spherical as polarisation ccurs so covalent character is gained

cation distrots -ve ions electron cloud due to polarisation

Question 17

entropy units

Answer 17

J K-1 Mol-1

Question 18

what is entropy at 0k

Answer 18

0 as particles dont move and are in max state or order

Question 19

change in S(total)

Answer 19

change in S(system) + change in S(surrounding)

Question 20

change in S(system)

Answer 20

sum of change in S for products - sum of change in S for reactants

Question 21

change in S surrounding =

Answer 21

minus change in enthalpy over temp

change in enthalpy units JMol-1

Question 22

gibbs free energy

Answer 22

change in enthalpy - (Temp x change in S(system) /1000)

as S is in J MOl-1

Question 23

second gibbs free energy equation

Answer 23

= -R T lnK

Question 24

when is a reaction feasible

Answer 24

when gibbs free energy is equal or less than 0

Question 25

atomisation

Answer 25

Standard enthalpy of atomisation: Enthalpy change when 1 mole of gaseous atoms is formed from
the elements in its standard states. Always endothermic

Question 26

lattic enethalpy

Answer 26

Standard lattice energy: Energy change when 1 mole of an ionic solid is formed from its constituent
gaseous ions under standard conditions

Question 27

electron affinity

Answer 27

First electron affinity: ​the enthalpy change that takes place when one electron is added to each
atom in one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 28

hyrdation

Answer 28

Enthalpy change of hydration ​: The enthalpy change when 1 mole of a gaseous ion is completely
dissolved in water under standard conditions. to infinite dilution

Question 29

solution

Answer 29

Enthalpy change of solution ​: Enthalpy change when 1 mole of ionic solid completely dissolves in
water under standard conditions to form an infinitely dilute solution.