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AL. OCR Chemistry > Enthalpy > Flashcards

Enthalpy Flashcards

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1
Q

enthalpy of formation

A

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

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2
Q

enthalpy of combustion

A

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

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3
Q

enthalpy of neutralisation

A

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

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4
Q

ionisation enthalpy (first)

A

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

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5
Q

ionisation enthalpy (second)

A

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

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6
Q 
electron affinity (first)
exo/endo?
A

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

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7
Q

electron affinity (second)

A

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

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8
Q

enthalpy of atomisation

A

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

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9
Q

hydration enthalpy

A

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

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10
Q

enthalpy of solution

A

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

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11
Q

bond dissociation enthalpy

A

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

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12
Q

lattice enthalpy of formation

A

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

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13
Q

lattice enthalpy of dissociation

A

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

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14
Q

enthalpy of vaporisation

A

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

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15
Q

enthalpy of fusion

A

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

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16
Q

average bond enthalpy

A

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

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17
Q

bond dissociation enthalpy

A

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

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18
Q

overall enthalpy change (eq)

A

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

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19
Q

Hess’ law

A

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

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20
Q

symbol for enthalpy

A

H

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21
Q

units of enthalpy

A

kJmol-1

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22
Q

value of ΔH when reaction is exothermic

A

negative

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23
Q

value of ΔH when reaction is endothermic

A

positive

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24
Q

enthalpy

A

energy stored within the bonds

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25
Q

standard lattice enthalpy

A

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

26
Q

standard conditions

A

298K

100Pa

27
Q 
standard lattice enthalpy is a measure of....
more negative (exothermic) the value the...
A

ionic bond strength

the stronger the bonding

28
Q

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

A

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

29
Q

higher the charge of the ions involved in lattice enthalpy…

A

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

30
Q

standard state

A

physical state under standard conditions

31
Q

bond making….. energy

A

releases (exothermic)

32
Q

bond breaking…. energy

A

requires (endothermic)

33
Q

collision theory

A

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

34
Q

(eq) percentage error

A

= error in measurement / measurement taken x 100

35
Q

gibs free energy

A

ΔG = ΔH-TΔS

36
Q

value of gibs energy when reaction is feasible

A

negative

37
Q

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

A

because values used are averaged across range of molecules

exact values depend on particular environment/molecule

38
Q

potential disadvantages of catalysts (2)

A
  • toxic

- expensive

39
Q

average bond enthalpy is a measure of …

A

average strength of a covalent bond

40
Q

enthalpy of reaction

A

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

41
Q

q =

A

Mc Δ T

42
Q

experimental method for investigating ΔH combustion of methanol

A
  • 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
43
Q

what does q stand for in q=mcΔt

A

energy change

44
Q

experimental method for investigating ΔHr for 2 liquids/solutions

A

use polystyrene cup

45
Q

entropy

A

dispersal of energy in a system and how disordered it is

46
Q

standard entropy

A

entropy of one mol of substance under standard conditions

47
Q

units of entropy

A

J/K/Mol

48
Q

feasibility

A

whether a reaction can happen or not

49
Q

free energy

A

overall energy change during a chemical reaction

50
Q

free energy equation

A

ΔG = ΔH - TΔS

51
Q

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

A

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

52
Q

factors affecting lattice enthalpy

A
  • ionic radius

- ionic charge

53
Q

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

A

hydration>lattice

54
Q

predict difference in hydration enthalpies of F- and Cl-

A

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

55
Q

another way of calculating ΔH

A

q (energy) / moles

56
Q

why is first election affinity sometimes positive

A

it takes energy to overcome repulsive intermolecular forces

57
Q

why may experimental enthalpy value be different to predicted?

A
  • some heat lost to surroundings not just to water
  • incomplete combustion - CO not CO2
  • evaporation of methanol from wick
  • non standard conditions
58
Q

bond enthalpies are always…

A

ENDOthermic

59
Q

to dissolve..

A

HYRDATION enthalpy&raquo_space;> LATICE enthalpy

60
Q

entropy equation

A

products - reactants

61
Q

free energy

A

overall energy change In a reaction

62
Q

limitations of feasibility w gibbs (2)

some reactions may not appear to occur as…

A
  • large activation energy

- slow rate

AL. OCR Chemistry (20 decks)

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