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Georges chem > enthalpy and entropy chp 22 > Flashcards

enthalpy and entropy chp 22 Flashcards

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1
Q

what is lattice enthalpy

A

the enthalpy change that accompanies the formation of 1 mole of an ionic compound from its gaseous ions under stand conditions

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2
Q

what type of reaction is lattice enthalpy and what does this mean for lattice enthalpy values

A
  • it is an exothermic change
  • the value for the enthalpy change will always be negative
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3
Q

what is needed to determine lattice enthalpy

A
  • it cannot be measured directly
  • you must use a Born-Hater cycle to determine it
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4
Q

what is the standard enthalpy change of atomisation

A
  • ΔatH
  • the enthalpy change that takes place for the formation of 1 mole of gaseous atoms from the element in its standard state under standard conditions
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5
Q

what type of value will ΔatH always give and why is that

A
  • it is always an endothermic process
  • ^because bonds are broken to form gaseous ions
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6
Q

what is the first ionisation energy

A
  • ΔieH
  • the enthalpy change required to remove one electron from each atom in 1 mole of gaseous atoms to form 1 mole of gaseous 1+ ions
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7
Q

what type of value will the ionisation energies also result in and why is this

A

ionisation energies are endothermic because energy is required to overcome the attraction between a negative electron and the positive nucleus

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8
Q

what is meant by electron affinity

A
  • it is the opposite of ionisation energy
  • electron affinity measures the energy to gain electrons
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9
Q

what is the first electron affinity in terms of enthalpy
what is it symbol

A
  • ΔeaH
  • the enthalpy change that takes place when 1 electron is added to each atom in 1 mole of gaseous atoms to from 1 mole of gaseous 1- ions
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10
Q

what type of value does first electron affinity always give and why is this

A
  • gives exothermic values
    ^because the electron being added is attracted in towards the nucleus
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11
Q

what type of value does second electron affinity always give and why is this

A
  • second electron affinities are endothermic
  • a second electron is being gained by a negative ion, which repels the electron away, so energy must be put in to force the like charges of the electron and the ion together
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12
Q

what is the standard enthalpy change of solution

A
  • ΔsolH
  • the enthalpy change that takes place when 1 mole of a solute dissolves in a solvent
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13
Q

what 2 processes occurs when a solid ionic compound dissolves in water

A
  • the ionic lattice breaks up
  • water molecules are attracted to, and surround, the ions
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14
Q

what 2 types of energy change are involved during a solid ionic compound dissolving in water

A
  • ionic lattice is broken up forming separate gaseous ions (opposite energy change from lattice energy)
  • separate gaseous ions interact with polar water molecules to form hydrated aqueous ions (enthalpy change of hydration)
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15
Q

what is the enthalpy change of hydration
whats its symbol

A
  • Δhyd H
  • enthalpy change that accompanies the dissolving of gaseous ions in water to form 1 mole of aqueous ions
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16
Q

what are the general properties of ionic compounds

A
  • high melting and boiling points
  • soluble in polar solvents
  • conduct electricity when molten or when aqueous
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17
Q

what does the value of lattice enthalpies depend upon

A
  • ionic size
  • ionic charge
18
Q

what is the effect of ionic size on lattice enthalpies

A
19
Q

what is the effect of ionic charge on lattice enthalpies

A
  • as ionic charge increases enthalpy value becomes more exothermic
    ^attraction between ions increases
    ^melting point increases
20
Q

What are sone factors that effect hydration enthalpies

A
  • ionic size
  • ionic charge
21
Q

what is the effect of ionic size on hydration enthalpies

A
22
Q

what is the effect of ionic charge on hydration enthalpies

A
23
Q

under what conditions should an ionic compound dissolve

A

if the sum of the hydration enthalpies is larger than the magnitude of the lattice enthalpy, the overall enthalpy change (enthalpy change of solution) will be exothermic and the compound should dissolve

24
Q

explain the chemistry as to why ionic liquids are liquid

A
  • ionic compounds have regularly shaped ions of similar size so they can pack together closely
  • ionic liquids have irregular shaped ions of different sizes, they are unable to pack together closely and so are liquid at room temp
25
Q

what is the symbol used to represent entropy, what units are used

A
  • S
  • J K^-1mol^-1
26
Q
  • define entropy
  • what it meant by high entropy
A
  • the dispersal of energy within chemicals making up a chemical system
  • greater the entropy, the greater the dispersal of energy and the greater the disorder
27
Q

what state of matter has the most and least entropy

A
  • solids have the smallest entropies
  • liquids have greater entropies
  • gases have the greatest entropies
28
Q

what would the entropy value of a chemical system by at 0 kelvin and above 0 kelvin

A
  • everything would have a entropy value of 0 at 0 K
  • above 0 K every value would be positive
29
Q

how will the entropy change be effect if a system changes to become more or less random

A
  • if a system becomes more random, energy can be spread out more ( entropy change will be positive)
  • if a system becomes less random, energy becomes more concentrated (entropy change will be negative)
30
Q

how could you predict wether entropy increases or decreases in an equation

A
  • by comparing the number of moles of gaseous molecules and physcial states of reactants and products
31
Q

under what conditions would entropy increase in an equation

A
  • if there is a change in state to give a more random arrangement of particles
  • melting and boiling increases the randomness of particles
  • energy is spread out more and Δ s is positive
32
Q

what is the standard entropy, what is a characteristics of its values

A
  • the entropy of 1 mole of a substance, under standard conditions
  • standard entropies are always positive
33
Q

how can the entropy change of reaction be calculated

A
34
Q

when can a reaction occur

A

if the products have a lower overall energy than the reactants

35
Q

what is meant by feasibility in chemistry

A
  • wether a reaction is able to happen and is energetically feasible (spontaneous may also be used)
36
Q

what is meant by the free energy change

what is its symbol

A
  • ΔG
  • the overall change in energy during a chemical reaction
37
Q

what 2 types of energy makes up free energy change

A
  • enthalpy change (the heat transfer between the chemical system and the surroundings)
  • entropy change at temperature of reaction
    ^this is the dispersal of energy within the chemical system itself
38
Q

what is the Gibbs equation

A
39
Q

what condition must be met for a reaction to be considered feasible

A
  • free energy change must be less than 0
40
Q

what units are entropy change of system (ΔS)

A
  • J K^-1mol^-1
41
Q

what must be the unit of entropy change of the system (ΔS) in the gibbs equation

A
  • Kj K^-1mol^-1
  • J K^-1mol^-1 / 1000 to find this
42
Q

what are the limitations of predictions made using feasibility

A
  • it doesn’t take into account kinetics and rate of reaction
    ^ large activation energies result in slow rates

Georges chem (29 decks)

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