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Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

define enthalpy change

A

amount of heat taken in or given out at constant pressure during any physical or chemical change

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2
Q

define standard enthalpy change

A

change in enthalpy when reactants in their standard states form products that are also in their standard states

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3
Q

define standard state

A

the state at a given temperature in its pure most stable form at 100kPa

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4
Q

when do exothermic changes occur

A

when forces of attraction operate

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5
Q

when do endothermic changes occur

A

when forces must be overcome/broken

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6
Q

define enthalpy of formation

A

enthalpy change when 1 mol of a substance is formed from its constituent elements with all substances in their standard states

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7
Q

define enthalpy of combustion

A

enthalpy change when 1 mol of substance undergoes complete combustion in O2 with all substances in their standard states

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8
Q

define enthalpy of neutralisation

A

enthalpy change when 1 mol of water is formed in a reaction between an acid and an alkali under standard conditions

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9
Q

define enthalpy of first ionisation

A

enthalpy change when each atom in 1 mol of gaseous atoms loses one electron to form one mol of gaseous 1+ ions

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10
Q

define enthalpy of second ionisation

A

enthalpy change when each ion in 1 mol of gaseous 1+ ions loses one electron to form one mol of gaseous 2+ ions

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11
Q

define enthalpy of first electron affinity

A

enthalpy change when each atom in 1 mol of gaseous atoms gains one electron to form one mol of gaseous 1- ions

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12
Q

define enthalpy of second electron affinity

A

enthalpy change when each atom in one mol of gaseous 1- ions gains one electron to form one mol of gaseous 2- ions

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13
Q

define enthalpy of atomisation

A

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

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14
Q

define hydration enthalpy

A

enthalpy change when 1 mol of gaseous ions become hydrated ( dissolved in water)

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15
Q

define enthalpy of solution

A

enthalpy change when 1 mol of ionic solid dissolves in amount of water large enough that dissolved ions are well separated and do not interact with each other

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16
Q

define bond dissociation enthalpy

A

enthalpy change when 1 mol of covalent bonds are broken in the gaseous state

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17
Q

define lattice enthalpy of formation

A

enthalpy change when 1 mol of a solid ionic compound is formed from its constituent ions in the gaseous phase

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18
Q

define lattice enthalpy of dissociation

A

enthalpy change when 1 mol of a solid ionic compound is broken up into its constituent ions in the gas phase

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19
Q

define enthalpy of vaporisation

A

enthalpy change when 1 mol of liquid is turned into gas

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20
Q

define enthalpy of fusion

A

enthalpy change when 1 mol of a solid is turned into a liquid

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21
Q

is enthalpy of formation endo of exothermic

A

mostly exothermic

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22
Q

is enthalpy of combustion endo or exothermic

A

exothermic

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23
Q

is enthalpy of neutralisation exo or endothermic

A

exothermic

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24
Q

is enthalpy of ionisation endo or exothermic

A

endothermic

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25
Q

is enthalpy of first electron affinity endo or exothermic

A

exothermic

26
Q

is enthalpy of second electron affinity endo or exothermic

A

endothermic

27
Q

is enthalpy of atomisation endo or exothermic

A

endothermic

28
Q

is enthalpy of hydration endo or exothermic

A

exothermic

29
Q

is enthalpy of solution endo or exothermic

A

varies

30
Q

is bond dissociation enthalpy endo or exothermic

A

endothermic

31
Q

is lattice enthalpy of formation endo or exothermic

A

exothermic

32
Q

is lattice enthalpy of dissociation exo or endothermic

A

endothermic

33
Q

is enthalpy of vaporisation endo or exothermic

A

endothermic

34
Q

is enthalpy of fusion endo or exothermic

A

endothermic

35
Q

what unknown enthalpy does a born-Haber cycle usually calculate

A

lattice enthalpy

36
Q

common mistakes to make in Born-Haber cycles

A

using wrong enthalpy changes
not multiplying by molar amounts
not taking care with signs

37
Q

what does enthalpy of formation equal in most Born-Haber cycles

A

sum of all other enthalpy values

38
Q

what do theoretical values for lattice enthalpies assume

A

perfect ionic model - all ions in an ionic compound are perfectly spherical

39
Q

are positive ions better at distorting negative ions when they’re larger or smaller, and with a higher or lower charge

A

small. higher charge.

40
Q

are negative ions easier to distort when they’re larger or smaller, and a higher or lower

A

larger and higher charge

41
Q

are ionic compounds with covalent characters more or less soluble in water

A

less soluble

42
Q

do ionic compounds with covalent characters have a higher or lower than expected melting point

A

lower than expected

43
Q

do ionic compounds with covalent character have higher or lower electrical conductivity than expected

A

lower than expected

44
Q

define magnitude of lattice enthalpy

A

overall strength of ionic bonding

45
Q

what does the difference between experimental and theoretical values in Born-Haber calculations mean

A

the larger the difference the more covalent character the ions possess

46
Q

are water molecules polar or nonpolar

A

polar

47
Q

is water attracted to anions, cations or neither

A

anions and cations

48
Q

is the hydration enthalpy larger or smaller for an ion with a higher charge-to-size ratio

A

larger

49
Q

what is entropy a measure of

A

the amount of disorder in a system

50
Q

when is the entropy value always zero

A

at 0K in a perfectly ordered crystal

51
Q

is enthalpy of the universe always increasing or decreasing

A

increasing

52
Q

what makes entropy increase

A

increase in temperature
from solid to liquid to gas
from simple to more complex molecules

53
Q

define feasible (spontaneous) change

A

one that has a natural tendency to occur without being driven by external influences

54
Q

at what free Gibbs energy value is a reaction at equilibrium

A

0

55
Q

at what free Gibbs value is a reaction feasible

A

deltaG

56
Q

how to find a feasible temperature at which a reaction can happen

A

set the free Gibbs value to 0 and solve for T

57
Q

Gibbs free energy equation symbol equation

A

deltaG = deltaH - TdeltaS

58
Q

acronym???? to remember Gibbs free energy equation

A

Grapes Have Tiny Seeds

59
Q

word equation for Gibbs free energy

A

Gibbs free energy change = enthalpy change - temperature X entropy change

60
Q

units for numbers used in Gibbs free energy equation

A

Gibbs free energy change in kJ/mol
enthalpy change in kJ/mol
temperature in Kelvin
entropy change in J/K/mol

61
Q

general graphical equation of Gibbs free energy

A

y = mx+c

Chemistry (24 decks)

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