Enthalpy

Question 1

enthalpy of formation

Answer 1

enthalpy change when one mole of a substance is formed form its constituent elements with all substances in their standard conditions
- exothermic (generally)

Question 2

enthalpy of combustion

Answer 2

enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states
- exothermic

Question 3

enthalpy of neutralisation

Answer 3

enthalpy change when 1 mole of WATER is formed in a reaction between an acid and an alkali under standard conditions
- exothermic

Question 4

ionisation enthalpy (first)

Answer 4

enthalpy change when one mole of gaseous atoms loosed one election to from one more of gaseous 1+ ions
- endothermic

Question 5

ionisation enthalpy (second)

Answer 5

enthalpy change when one mole of gaseous 1+ ions loosed one election to from one more of gaseous 2+ ions
- endothermic

Question 6

electron affinity (first)
exo/endo?

Answer 6

enthalpy change when each atom in one mole of gaseous atoms gains one electron to become 1- ions
- exothermic

Question 7

electron affinity (second)

Answer 7

enthalpy change when each atom in one mole of gaseous 1- ions gains one electron to become 2- ions
- endothermic

Question 8

enthalpy of atomisation

Answer 8

enthalpy change when one mole of gaseous atoms is produced from an element in its standard state
- endothermic

Question 9

hydration enthalpy

Answer 9

enthalpy change when one mole of gaseous ions becomes hydrated (dissolves in water)
- exothermic

Question 10

enthalpy of solution

Answer 10

enthalpy change when one mole of an ionic solid dissolves in an amount of water large enough so that all the dissolved ions are well separated and do not interact with each other (dissociated ions)
-varies

Question 11

bond dissociation enthalpy

Answer 11

enthalpy change when one mole of covalent bonds is broken in the gaseous state
- endothermic

Question 12

lattice enthalpy of formation

Answer 12

enthalpy change when one mole of a solid ionic compound is formed from its constituent ions in GAS state
- exothermic

Question 13

lattice enthalpy of dissociation

Answer 13

enthalpy change when one mole of solid ionic compound is broken up into its constituent ions in their GAS state
- endothermic

Question 14

enthalpy of vaporisation

Answer 14

energy change when one mole of a liquid is turned into a gas
- endothermic

Question 15

enthalpy of fusion

Answer 15

energy change when one mole of a solid is turned into a liquid
- endothermic

Question 16

average bond enthalpy

Answer 16

the average enthalpy change that takes place when breaking by homiletic fission 1 mol of a given type of bond in the molecules of a gaseous species

Question 17

bond dissociation enthalpy

Answer 17

the enthalpy change when 1 mol of a given bond in the molecules of a gaseous species is broken by homiletic fission

Question 18

overall enthalpy change (eq)

Answer 18

[sum of enthalpy of formation product] - [sum of enthalpy of formation of reactants]

Question 19

Hess’ law

Answer 19

if a reaction takes place by 2 routes, and starting and finishing conditions are the same the total enthalpy change will be the same for each route

Question 20

symbol for enthalpy

Answer 20

H

Question 21

units of enthalpy

Answer 21

kJmol-1

Question 22

value of ΔH when reaction is exothermic

Answer 22

negative

Question 23

value of ΔH when reaction is endothermic

Answer 23

positive

Question 24

enthalpy

Answer 24

energy stored within the bonds

Question 25

standard lattice enthalpy

Answer 25

energy change when 1 mole of an ionic lattice is formed from gaseous ions under standard conditions

Question 26

standard conditions

Answer 26

298K | 100Pa

Question 27

``` standard lattice enthalpy is a measure of.... more negative (exothermic) the value the... ```

Answer 27

ionic bond strength | the stronger the bonding

Question 28

smaller the ionic radius of the ions involved in lattice enthalpy...

Answer 28

more exothermic - higher charge density and smaller radius means ions can sit closer together making attractions between ions stronger

Question 29

higher the charge of the ions involved in lattice enthalpy...

Answer 29

more exothermic - more energy released when lattice forms as stronger electrostatic attraction between ions

Question 30

standard state

Answer 30

physical state under standard conditions

Question 31

bond making..... energy

Answer 31

releases (exothermic)

Question 32

bond breaking.... energy

Answer 32

requires (endothermic)

Question 33

collision theory

Answer 33

in order for parties to react, they must collide in the right direction and orientation with a minimum amount of kinetic energy

Question 34

(eq) percentage error

Answer 34

= error in measurement / measurement taken x 100

Question 35

gibs free energy

Answer 35

ΔG = ΔH-TΔS

Question 36

value of gibs energy when reaction is feasible

Answer 36

negative

Question 37

why might calculated enthalpy change may not be the same as experimental value?

Answer 37

because values used are averaged across range of molecules | exact values depend on particular environment/molecule

Question 38

potential disadvantages of catalysts (2)

Answer 38

- toxic | - expensive

Question 39

average bond enthalpy is a measure of ...

Answer 39

average strength of a covalent bond

Question 40

enthalpy of reaction

Answer 40

enthalpy change accompanying reaction in molar quantities shown in chemical equation under standard conditions with all reactants and products in standard states

Question 41

q =

Answer 41

Mc Δ T

Question 42

experimental method for investigating ΔH combustion of methanol

Answer 42

- add methanol to spirit burner and weigh - place unde breaker of 150cm3 water - measured usingg measuring cylinder - record initial temp of water - light spirit burner and leave for 3 mins - extinguish flame and immediately record highest temp reached - reweigh spirit burner

Question 43

what does q stand for in q=mcΔt

Answer 43

energy change

Question 44

experimental method for investigating ΔHr for 2 liquids/solutions

Answer 44

use polystyrene cup

Question 45

entropy

Answer 45

dispersal of energy in a system and how disordered it is

Question 46

standard entropy

Answer 46

entropy of one mol of substance under standard conditions

Question 47

units of entropy

Answer 47

J/K/Mol

Question 48

feasibility

Answer 48

whether a reaction can happen or not

Question 49

free energy

Answer 49

overall energy change during a chemical reaction

Question 50

free energy equation

Answer 50

ΔG = ΔH - TΔS

Question 51

Why might some reactions not appear to take place even though free energy is negative?

Answer 51

because rate isn't taken into account - rate may be so slow reaction does not appear to be happeneing

Question 52

factors affecting lattice enthalpy

Answer 52

- ionic radius | - ionic charge

Question 53

when (in terms of enthalpy) will a substance dissolve?

Answer 53

hydration>lattice

Question 54

predict difference in hydration enthalpies of F- and Cl-

Answer 54

F- will me more negative as smaller atomic radius smaller sized ion has greater attraction to H2O

Question 55

another way of calculating ΔH

Answer 55

q (energy) / moles

Question 56

why is first election affinity sometimes positive

Answer 56

it takes energy to overcome repulsive intermolecular forces

Question 57

why may experimental enthalpy value be different to predicted?

Answer 57

- some heat lost to surroundings not just to water - incomplete combustion - CO not CO2 - evaporation of methanol from wick - non standard conditions

Question 58

bond enthalpies are always...

Answer 58

ENDOthermic

Question 59

to dissolve..

Answer 59

HYRDATION enthalpy >>> LATICE enthalpy

Question 60

entropy equation

Answer 60

products - reactants

Question 61

free energy

Answer 61

overall energy change In a reaction

Question 62

limitations of feasibility w gibbs (2) | some reactions may not appear to occur as...

Answer 62

- large activation energy | - slow rate