Energetics

Question 1

define enthalpy change of atomisation ∆Hat

Answer 1

the energy change of turning one mole of gaseous atoms is formed form its element under standard condition.

Question 2

is ∆Hat exothermic or endothermic

Answer 2

always endothermic — positive

Question 3

define enthalpy change of hydration ∆Hhyd

Answer 3

energy change when one mole of gaseous ions are dissolved in sufficient water to create an infinitely diluted solution

Question 4

∆Hhyd exo or endo

Answer 4

always exothermic — negative

Question 5

define lattice enthalpy ∆Hlat

Answer 5

the enthalpy change of one mole of an ionic lattice is formed from its isolated gaseous ions under standard state

Question 6

is ∆Hlat exo or endo

Answer 6

always enxothermic — negative

Question 7

define first electron affinity Eea(I)

Answer 7

energy released when one mole of electron is added to one mole of gaseous atoms to form one mole of gaseous 1- ions

Question 8

is Eea (I) endo or exo

Answer 8

always exothermic — negative

Question 9

is second Eea endo or exo

Answer 9

always endothermic — positive

Question 10

why is second Eea endothermic

Answer 10

because adding an electron to an already negative ion causes repulsion => needs energy

Question 11

define enthalpy of solution ∆Hsoln

Answer 11

energy change when one mole of a solute dissolves in a solvent to give an infinitely dilute solution under standard condition

Question 12

define entropy S

Answer 12

the number of possible arrangement of the particles and their energy in a given system

Question 13

why is ∆Hhyd exo

Answer 13

because more intermolecular bonds form as gas turn aqueous

Question 14

why is ∆Hat endo

Answer 14

bond breaks within element therefore endo

Question 15

does small ∆Hhyd mean more soluble for less

Answer 15

small value means more soluble

Question 16

sate the relation between enthalpy change of hydration, solution and lattice

Answer 16

∆Hhyd =∆Hlat + ∆Hsoln

Question 17

what is standard condition

Answer 17

1 atmospheric pressure: 101 k pascal
1 moldm^-3
298 kelvin = 25 C

Question 18

how to find the enthalpy change using bond energy

Answer 18

sum of all bond energy of product - sum of all bond energy of reactant

Question 19

calculate ∆S (system)

Answer 19

∆S = S product - S reactant

Question 20

equation for change of energy

Answer 20

Q = - m c ∆T (negative!!!!!!)

Question 21

how does ∆H defer from Q

Answer 21

∆H = Q/mole

Question 22

how does increase in temp effect entropy

Answer 22

temp incr => entropy incr

Question 23

which physical state has higher entropy

Answer 23

solid < liquid < gas

Question 24

decrease in moles of gas implies

Answer 24

decrease of entropy

Question 25

what are the factors that effect the ∆Hhyd

Answer 25

1. size of the ion (radius) 2. size of the charge (2- or 1-, etc)

Question 26

explain how does the size of ion effect ∆Hhyd

Answer 26

increase size of ion => increased distance between the ion & more shells of electron create more shielding => decrease in bond strength => more soluble => less exothermic

Question 27

explain how does the size of charge effect ∆Hhyd

Answer 27

increase in charge (2- instead of 1-) => larger charge density (this is key word) => stronger attraction in the ionic lattice => more exothermic

Question 28

define feasible reaction

Answer 28

"energetically favourable but kinetically unfavourable"

Question 29

∆S of feasible is

Answer 29

positive

Question 30

∆G of feasible is

Answer 30

negative

Question 31

what is unit for S

Answer 31

J k^-1

Question 32

what gibbs Free energy change

Answer 32

∆G = ∆H - T ∆S

Question 33

what does it mean for the reaction to cease to become feasible

Answer 33

∆G = 0 ===> ∆H = T ∆J