Thermodynamics

Question 1

Define Enthalpy change of Formation?

Answer 1

⦾ ΔH1
⦾ ΔHf
⦾ ΔH when 1 mole of compound is formed from its elements in their standard states

Question 2

Define Bond Dissociation Enthalpy?

Answer 2

⦾ ΔHdiss

⦾ ΔH when all the bonds of the same type in 1 mole of gaseous molecules are broken

Question 3

Define Enthalpy change of Atomisation of an element?

Answer 3

⦾ ΔH2 + ΔH3
⦾ ΔHat
⦾ ΔH when 1 mole of a compound in its standard states is converted to gaseous atoms

Question 4

Define First Ionisation Energy?

Answer 4

⦾ ΔH4
⦾ ΔHie1
⦾ ΔH when 1 mole of a gaseous 1+ ions is formed from 1 mole gaseous atoms

Question 5

Define Second Ionisation Energy?

Answer 5

⦾ ΔHie2

⦾ ΔH when 1 mole of gaseous 2+ ions is formed from 1 mole of gaseous 1+ ions.

Question 6

Define First Electron Affinity?

Answer 6

⦾ ΔH5
⦾ ΔHea1
⦾ ΔH when 1 mole of gaseous 1- ions is formed from 1 mole of gaseous atoms.

Question 7

Define Second Electron Affinity?

Answer 7

⦾ ΔHea2

⦾ ΔH when 1 mole of gaseous 1- ions gains 1 electron per ion to produce gaseous 2- ions

Question 8

Define Lattice enthalpy of Formation?

Answer 8

⦾ ΔH6
⦾ ΔHlattice
⦾ ΔH when 1 mole of solid ionic compound is formed from its gaseous ions

Question 9

Define Lattice enthalpy of Dissociation?

Answer 9

⦾ ΔHlattice
⦾ ΔH when 1 mole of solid ionic compound is completely dissociated into gaseous ions
⦾ Endothermic

Question 10

Define Enthalpy change of Hydration?

Answer 10

⦾ ΔHhyd
⦾ ΔH when 1 mole of aqueous ions is formed from gaseous ions
⦾ Exothermic

Question 11

Define Enthalpy change of Solution?

Answer 11

⦾ ΔHsolution

⦾ ΔH when 1 mole of ionic substance dissolves in enough solvent to form an infinitely dilute solution

Question 12

What is an infinitely dilute solution?

Answer 12

⦾ Contains so much solvent that when more liquid is added, there is no change in concentration.

Question 13

What is Hess’s Law?

Answer 13

⦾ Total enthalpy change of a reaction is the same no matter the route taken

Question 14

How do you calculate ΔH6?

Answer 14

⦾ ΔH6 = - (ΔH5) - (ΔH4) - (ΔH3) - (ΔH2) + (ΔH1)

Question 15

How do you calculate ΔH1?

Answer 15

⦾ ΔH1 = (ΔH2) + (ΔH3) + (ΔH4) + (ΔH5) + (ΔH6)

Question 16

What must you do if you go the wrong way along an arrow?

Answer 16

⦾ Add in a minus sign

Question 17

What does the purely ionic model of a lattice assume?

Answer 17

⦾ All ions are spherical

⦾ Have their charge evenly distributed around them

Question 18

How can water form bonds with ionic lattices?

Answer 18

⦾ Water's polar molecule
⦾ O more electronegative than H
⦾ So draws bonding electrons towards itself creating dipole
⦾ +ve ions form weak bonds with O 
⦾ -ve ions form weak bond with H

Question 19

What is the enthalpy change of solution?

Answer 19

⦾ Overall effect of enthalpy of bond breaking and making.

Question 20

What do you need to know to work out the ethalpy change of a solution using an enthalpy cycle?

Answer 20

⦾ Lattice dissociation enthalpy of the compound
⦾ Enthalpies of hydration of ions
⦾ ΔH3 = ΔH1 + ΔH2

Question 21

What does ‘entropy’ mean?

Answer 21

⦾ How much disorder

⦾ Measure of no. of ways particles arranged and no. of ways energy can be shared out between particles

Question 22

State the factors that affect entropy?

Answer 22

1 ⦾ Physical state
2 ⦾ Dissolution
3 ⦾ No. of particles

Question 23

How does physical state affect entropy?

Answer 23

⦾ Solids fixed in place so least entropy

⦾ Gases bounce in random movement so most entropy

Question 24

How does Dissolution affect entropy?

Answer 24

⦾ Dissolving solid increased its entropy

⦾ Free to move - no longer held in place

Question 25

How does no. of particles affect entropy?

Answer 25

⦾ More particles means more entropy

⦾ More ways energy’s arranged

Question 26

When water evaporate, entropy…

Answer 26

⦾ …increases

⦾ Change from liquid to gas

Question 27

When NaHCO3 and HCl react, entropy…

Answer 27

⦾ Increases
⦾ More particles in product
⦾ NaHCO3(s) + H+(aq) ➜ Na+(aq) + CO2(g) + H2O(l)

Question 28

What is the formula for calculating entropy changes?

Answer 28

⦾ ΔS = Sproducts - Sreactants

Question 29

What are the units for entropy?

Answer 29

⦾ J/K/mol

Question 30

What is Free-energy change?

Answer 30

⦾ ΔG is measure to predict whether certian reaction is feasible

Question 31

What is a feasible reaction?

Answer 31

⦾ Reaction that once started will continue onto completion, without any energy being supplied to it

Question 32

What does it mean if ΔG is -ve or equal to zero?

Answer 32

⦾ Reaction is feasible

Question 33

What is the formula for calculating free-energy change (ΔG)?

Answer 33

⦾ ΔG = ΔH - TΔS
⦾ ΔG = Free-energy change (J/mol)
⦾ ΔH = Enthalpy change (J/mol)
⦾ T = Temp (K) ΔS = Entropy change (J/K/mol)

Question 34

Why might a -ve ΔG not guarantee a reaction will happen or tell you about the rate?

Answer 34

⦾ May have a very high activation energy

⦾ So slow you wouldn’t notice it happening

Question 35

If a reaction is exothermic (-ΔH) and has a +ve entropy change, then the ΔG is always…

Answer 35

⦾ … -ve

⦾ These reactions are feasible at any temperature

Question 36

If a reaction is endothermic (+ΔH) and has a -ve entropy change, then the ΔG is always…

Answer 36

⦾ … +ve

⦾ These reactions aren’t feasible at any temperature

Question 37

If a reaction ΔH is positive (endothermic) and ΔS is positive, then the reaction will only be feasible…

Answer 37

⦾ …above a certain temperature

Question 38

If a reaction ΔH is negative (exothermic) and ΔS is negative, then the reaction will only be feasible…

Answer 38

⦾ … below a certain temperature