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Physical Chemistry > Thermodynamics > Flashcards

Thermodynamics Flashcards

1
Q

define enthalpy change

A

the heat energy change at constant pressure

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2
Q

define standard enthalpy of formation

A

the enthalpy change when one mole of a substance is formed from its elements under standard conditions with all substances in their standard states

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3
Q

define standard enthalpy of combustion

A

the enthalpy change when one mole of a substance is completely combusted in excess oxygen under standard conditions with all substances in their standard states

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4
Q

define mean bond enthalpy

A

the enthalpy change when one mole of a given covalent bond is broken averaged over a range of compounds

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4
Q

define standard enthalpy of atomisation

A

the enthalpy change for the formation of one mole of gaseous atoms from the element in its standard state

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5
Q

define bond dissociation enthalpy

A

the enthalpy change to break the bond in one mole of gaseous molecules to form gaseous atoms

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6
Q

define first ionisation energy

A

the enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to form one mole of gaseous 1+ ions

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7
Q

define second ionisation energy

A

the enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions

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8
Q

define lattice formation enthalpy

A

the enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions

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8
Q

define first electron affinity

A

the enthalpy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous 1- ions

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9
Q

define second electron affinity

A

the enthalpy change when one mole of electrons is added to one mole of 1- ions to form one mole of gaseous 2- ions

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10
Q

why is the second electron affinity of any ion always endothermic

A

due to the repulsion between the negative ion and negative electron, energy is required to overcome it

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11
Q

why is the second ionisation of an ion greater than the first

A

it is more difficult to remove an electron from a positive ion due to the stronger electrostatic attraction

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11
Q

define lattice dissociation enthalpy

A

the enthalpy change to separate one mole of solid ionic compound into its gaseous ions

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12
Q

how to calculate the standard enthalpy of atomisation for diatomic substances

A

bond dissociation enthalpy/2

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12
Q

why is the first electron affinity exothermic

A

due to the electrons attraction to the nucleus

13
Q

what does Bend-Mex mean

A
  • breaking bonds is endothermic
  • making bonds is exothermic
14
Q

how does the strength of attraction correlate with the lattice formation enthalpy

A
  • the stronger the attractions, the more exothermic the lattice formation enthalpy is
15
Q

how does the strength of attraction correlate with the lattice dissociation enthalpy

A
  • the stronger the attractions, the more endothermic the lattice dissociation enthalpy is
16
Q

how does ion charge affect lattice enthalpy

A
  • the higher the charge on the ion, the smaller the ionic radius will be meaning they are closer together in the lattice leading to a stronger ionic bond
  • stronger attraction means more energy is given out on the formation and more energy is needed to dissociate the lattice
17
Q

how does the size of ion affect lattice enthalpy

A
  • the smaller the ionic radius the closer together they are in the lattice leading to a stronger ionic bond
  • stronger attraction means more energy is given out on the formation and more energy is needed to dissociate the lattice
18
Q

what is the perfect ionic model

A
  • a model that assumes all ions are perfect spheres with purely ionic attraction
19
Q

how can you use the theoretical and experimental lattice enthalpy values to predict the ionic shape of a compound

A
  • if the experimental value is the same as the theoretical there is no covalent character and it is the perfect ionic model
  • if the experimental value differs from the theoretical it is due to the covalent character
20
Q

how is a covalent character formed

A
  • the cation is much smaller than the anion and/or is highly charged
  • the cation attracts the anion’s electrons causing the anion to become distorted and more covalent i.e. polarised
21
Q

how does a covalent character affect the strength of an ionic bond

A
  • with a covalent character, the ionic bond is stronger
22
Q

how does polarisation affect the experimental enthalpy of lattice formation

A

the experimental enthalpy of lattice formation will be more exothermic than the theoretical value

23
Q

how does polarisation affect the experimental enthalpy of lattice dissociation

A

Physical Chemistry (10 decks)

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