enthalpy and entropy chp 22

Question 1

what is lattice enthalpy

Answer 1

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

Question 2

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

Answer 2

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

Question 3

what is needed to determine lattice enthalpy

Answer 3

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

Question 4

what is the standard enthalpy change of atomisation

Answer 4

• 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

Question 5

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

Answer 5

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

Question 6

what is the first ionisation energy

Answer 6

• 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

Question 7

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

Answer 7

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

Question 8

what is meant by electron affinity

Answer 8

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

Question 9

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

Answer 9

• 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

Question 10

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

Answer 10

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

Question 11

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

Answer 11

• 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

Question 12

what is the standard enthalpy change of solution

Answer 12

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

Question 13

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

Answer 13

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

Question 14

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

Answer 14

• 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)

Question 15

what is the enthalpy change of hydration
whats its symbol

Answer 15

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

Question 16

what are the general properties of ionic compounds

Answer 16

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

Question 17

what does the value of lattice enthalpies depend upon

Answer 17

• ionic size
• ionic charge

Question 18

what is the effect of ionic size on lattice enthalpies

Answer 18

Question 19

what is the effect of ionic charge on lattice enthalpies

Answer 19

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

Question 20

What are sone factors that effect hydration enthalpies

Answer 20

• ionic size
• ionic charge

Question 21

what is the effect of ionic size on hydration enthalpies

Answer 21

Question 22

what is the effect of ionic charge on hydration enthalpies

Answer 22

Question 23

under what conditions should an ionic compound dissolve

Answer 23

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

Question 24

explain the chemistry as to why ionic liquids are liquid

Answer 24

• 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

Question 25

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

Answer 25

- S - J K^-1mol^-1

Question 26

- define entropy - what it meant by high entropy

Answer 26

- 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

Question 27

what state of matter has the most and least entropy

Answer 27

- solids have the smallest entropies - liquids have greater entropies - gases have the greatest entropies

Question 28

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

Answer 28

- everything would have a entropy value of 0 at 0 K - above 0 K every value would be positive

Question 29

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

Answer 29

- 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)

Question 30

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

Answer 30

- by comparing the number of moles of gaseous molecules and physcial states of reactants and products

Question 31

under what conditions would entropy increase in an equation

Answer 31

- 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

Question 32

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

Answer 32

- the entropy of 1 mole of a substance, under standard conditions - standard entropies are always positive

Question 33

how can the entropy change of reaction be calculated

Answer 33

Question 34

when can a reaction occur

Answer 34

if the products have a lower overall energy than the reactants

Question 35

what is meant by feasibility in chemistry

Answer 35

- wether a reaction is able to happen and is energetically feasible (spontaneous may also be used)

Question 36

what is meant by the free energy change | what is its symbol

Answer 36

- ΔG - the overall change in energy during a chemical reaction

Question 37

what 2 types of energy makes up free energy change

Answer 37

- 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

Question 38

what is the Gibbs equation

Answer 38

Question 39

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

Answer 39

- free energy change must be less than 0

Question 40

what units are entropy change of system (ΔS)

Answer 40

- J K^-1mol^-1

Question 41

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

Answer 41

- Kj K^-1mol^-1 - J K^-1mol^-1 / 1000 to find this

Question 42

what are the limitations of predictions made using feasibility

Answer 42

- it doesn't take into account kinetics and rate of reaction ^ large activation energies result in slow rates