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OCR CHEMISTRY A > x > Flashcards

x Flashcards

1
Q

lattice enthalpy definition

A

measure of the strength of ionic bonding in a giant ionic lattice

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2
Q

what is the purpose of Born- Haber cycles

A

determines the lattice enthalpy indirectly

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3
Q

what sort of energy change is needed to form gaseous atoms? why?

A
  • endothermic

- involves breaking bonds

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4
Q

what sort of energy change is needed to form gaseous ions?

A

endothermic

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5
Q

what sort of energy change is needed to form a lattice

A

exothermic

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6
Q

standard enthalpy change of formation definition

A

formation of 1 mol of a compound from its elements in its standard states under standard conditions

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7
Q

standard enthalpy change of atomisation definition

A

formation of one mole of gaseous atoms from the element in its standard states under standard conditions

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8
Q

first electron affinity definition

A

addition of 1 mol of electrons to 1 mol of gaseous atoms to form 1 mol of gaseous 1- ions

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9
Q

enthalpy change of hydration definition

A

dissolving of 1 mol of gaseous ions in water

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10
Q

explain why the 2nd ionisation is more endothermic than the 1st ionisation

A
  • Mg+ has one more proton than electrons
  • increase nuclear attraction
  • decrease radius
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11
Q

what energy is needed in the second electron affinity

A

enothermic

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12
Q

what energy is needed in the second electron affinity

A

endothermic

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13
Q

write the equation to calculate energy change

A

q=mc∆T

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14
Q

what 2 processes take place when ionic compounds dissolve in water

A
  • ionic lattice breaks up

- water molecules are attracted to, and surround, the ions

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15
Q

what are the general properties of ionic compounds?

A
  • high melting and boiling points
  • soluble in polar solvents
  • conduct electricity when molten or in aqueous solution
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16
Q

effect of ionic size on lattice enthalpy

A
  • ionic radius increases
  • attraction between ions decrease
  • lattice enthalpy less negative
  • melting point decreases
17
Q

effect of ionic charge on lattice enthalpy

A
  • ionic charge increases
  • attraction between ions increase
  • lattice energy becomes more negative
  • melting point increases
18
Q

effect of ionic charge size from left to right

A
  • increasing charge gives more attraction

- decreasing size gives more attraction

19
Q

effect of ionic charge size from right to left

A
  • increasing charge gives more attraction

- increasing size gives less attraction

20
Q

effect of ionic size on hydration enthalpy down group 1

A
  • ionic radius increases
  • attraction between ion and water molecules decreases
  • hydration energy less negative
21
Q

effect of ionic size on hydration enthalpy down group 1

A
  • ionic radius increases
  • attraction between ion and water molecules decreases
  • hydration energy less negative
22
Q

effect of ionic charge on hydration enthalpy

A
  • ionic charge increases
  • attraction with water molecules increases
  • hydration energy become more negative
23
Q

what can entropy be used to predict

A
  • a gas spreading through a room
  • heat from a fire spreading through a room
  • ice melting in a hot room
24
Q

general rules of entropy

A
  • solids have the smallest entropies
  • liquids have greater entropies
  • gases have the greatest entropies
25
Q

what will the entropy change be if a system changes to become more random

A
  • energy becomes more spread out

- ∆S is positive

26
Q

what will the entropy change be if a system changes to become less random

A
  • energy becomes more concentrated

- ∆S is negative

27
Q

when any substance changes state from solid to liquid to gas, its entropy increases:

A
  • melting and boiling increase the randomness of particles

- energy is spread out more and ∆S is positive

28
Q

describe the entropy of this reaction:

N₂(g) +3H₂(g) -> 2NH₃(g)

A
  • decrease in the randomness of particles

- energy is spread out less and ∆S is negative

29
Q

standard entropy of a substance

A

entropy of 1 mole of a substance, under standard conditions (100kPa and 298K)

30
Q

standard enthalpy facts

A
  • JK⁻¹mol⁻¹

- always positive

31
Q

calculate entropy changes

A

∆S=ΣS(products)-ΣS(reactants)

32
Q

calculate entropy changes

A

∆S=ΣS(products)-ΣS(reactants)

33
Q

write the Gibb’s equation

A

∆G=∆H-T∆S

34
Q

enthalpy change, ∆H

A

heat transfer between the chemical system and the surroundings

35
Q

entropy change at the temperature of the reaction, T∆S

A

dispersal of energy within the chemical system itself

36
Q

conditions for feasibility

A
  • ∆G<0
37
Q

limitations of predictions made for feasibility

A

rate of reaction is very slow

OCR CHEMISTRY A (34 decks)

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