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Chemistry OCR B Alevel > oceans > Flashcards

oceans Flashcards

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1
Q

what is lattice enthalpy?

A

the enthalpy change when 1 mole of solid is formed by the coming together of separate ions

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2
Q

what is the main enthalpy change that prevents a substance dissolving?

A

lattice enthalpy

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3
Q

what is the enthallpy change to split up an ionic compound into its ions?

A

negative lattice enthalpy

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4
Q

is the enthalpy chnage to split up an ionic compound exo or endo thermic?

A

endothermic, it is positive, requires energy

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5
Q

is lattice enthalpy exo or endothermic? and why?

A

exothermic as it makes ionic bonds

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6
Q

what is the enthaply change of hydration?

A

the enthalpy change for the formation of 1 mole of aqueous ions from 1 mole of gaseous ions

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7
Q

what bonds form between ions and molecules of water for it ti dissolve?

A

ion-diople interactions

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8
Q

is ethalpy change of hydration positive or negative? and why?

A

negative as hydration is exothermic due to ion-dipole bonds made

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9
Q

what effect does charge density have on the hydration enthalpy?

A

as charge density increases, there is greater attraction of water molecules so hydration enthalpy becomes more exothermic

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10
Q

what effect does charge density have on lattice enthalpy?

A

as charge density increases, there is greaer electrostatic attraction between ions so lattice enthalpy becomes more negative

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11
Q

what is a hydrated ion?

A

an ion with water molecules bound to them

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12
Q

what is the other version of enthalpy of hydration when the solvent isnt water?

A

enthalpy of solvation

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13
Q

what is the enthalpy change of solution?

A

the enthalpy change when one mole of an ionic solid becomes aqeous ionswhy

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14
Q

what is the equation for enthalpy chnage of solution?

A

sum of enthalpy change of hydration - lattice enthalpy

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15
Q

can a negative enthalpy change of solution dissolve?

A

yes

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16
Q

why can a slightly positiive enthalpy change of solution still dissolve?

A

due to entropy

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17
Q

what kind of enthalpy change of solution would occur if you dissolved an ionic compound in a non polar solvent?

A

very large positive

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18
Q

what is entropy?

A

a measure of the number of ways that molecules and their associated energy (electrons) can be arranged

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19
Q

what are the units of entropy?

A

JK-1mol-1

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20
Q

what are 2 factors that increase the entropy of a collection of molecules?

A

the molecules spread out more

the energy is shared among more molecules

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21
Q

place solid, liquid and gas in order of increasing enrpoy

A

soli liquid gas

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22
Q

what would make entropy change of system positive?

A

if there are more molecules of products than reactants,

if more molecules of products are gaseous than the reactants

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23
Q

what is the equation for the total entropy change for a process?

A

total entropy change = system entropy - surrounding entropy

24
Q

what is the equation for the entropy change of a system?

A

entropy of products - entropy of reactants

25
Q

what is the equation for entropy change of the surroundings?

A

entropy change of surroundings = - energy transferred/ temperature (k)

26
Q

For a spontaneous reaction what does total entropy change have to be?

A

positive

27
Q

even if total entropy change is positive, sometimes reaction does not happen, why is this?

A

activation energy is too high

rate of reaction is too slow

28
Q

what is a bronsted lowrey acid?

A

a proton donator

29
Q

what is a bronsted lowrey base?

A

A proton acceptor

30
Q

what is a strong acid?

A

acids that completely disscociate in water

31
Q

how can you calculate the pH of a strong acid?

A

you know that becuase it completely dissociates, |H+| = |HA| so just use the pH=-log|H+|

32
Q

what is the equation for pH?

A

pH= -log|H+|

33
Q

What is a weak acid?

A

an acid that partially dissociates in water, the level of dissociation is measured using Ka (acid constant/ acidity constant)

34
Q

what are 2 assumptions made to calculated pH of a weak acid?

A

only a small proportion of HA dissociates to
|HA| at the start = |HA| at equilibrium

assume that a negligible amount of water in solution dissociates so no H+ are provided by the water so
|H+| = |A-|

35
Q

What is the acid constant equation?

A

Ka = (|H+| |A-|)/|HA|

36
Q

How do you calculate the pH of a weak acid?

A

use Ka = |H+|^2 / |HA|

37
Q

What is the equation of pKa?

A

pKa= -logKa

38
Q

the lower the pKa the ________ the acid

A

stronger

39
Q

what is a strong base?

A

a base that fully dissociates in water

40
Q

what is the equation for Kw?

A

Kw= |H+| |OH-|

41
Q

How do you calculate the pH of a strong base?

A

use the Kw equation as |base|=|OH-|

42
Q

What is a buffer solution?

A

a solution of large amounts of weak acid and large amounts of the salt of this acid that will resist change in pH when small volumes of acid or alkali are added

43
Q

what happens when you add an alkali to a buffer solution?

A

it reacts with the H+ to form water so large amounts of HA dissociate to replace it
equilibrium shifts to the right

44
Q

what happens if you add an acid to a buffer solution?

A

large amounts of A- react with excess H+ to make HA

equilibrium shifts to the left

45
Q

what are 2 assumptions made in buffer calculations?

A

assume all |A-| has come from the salt

assume |HA| has no dissociate so
|HA| a start = |HA| at equilibrium

46
Q

how do you calculate pH of buffer solution?

A

use Ka equations to find |H+| then use pH equation

47
Q

what kind of radiation from the sun reaches the earths surface?

A

UV and light

48
Q

what happens when the earth absorbs UV?

A

it heats up and radiates infrared

49
Q

green house gases in the _________ absorb _________ ___________ radiated from the ______ and ______ some of it in __ ________
this is in the _______ _________

A

troposphere

infrared radiation

earth

reemit

all directions

infrared window

50
Q

how do green house gases raise the temperature of the atmosphere when they absorb infrared?

A

green house gases absorb the infrared radiation which causes their bonds to vibrate , this energy is transferred to other molecules by collision, increasing their kinetic energy and rasiing the overall temperature

51
Q

what are 3 greenhouse gases?

A

methane

co2

water vapour

52
Q

what makes a green house gas contribute to the green house effect more?

A

absorbing more radiation

being more abundant in the atmosphere

53
Q

what is Ksp?

A

solubility product

Ksp= |A-| |B+|

54
Q

If Ksp calculated is higher than actual Ksp?

A

precipitate will form

55
Q

What factors determine the pH of a buffer solution?

A

Ka /pKa /acid strength/amount of dissociation

temperature

ratio/concentrations of weak acid and
conjugate base/salt

Chemistry OCR B Alevel (14 decks)

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