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chemistry year 13 > 5.2 > Flashcards

5.2 Flashcards

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1
Q

what is an oxidising agent

A

a substance that oxidises another substance and in doing so becomes reduced

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2
Q

what is a reducing agent

A

a substance that reduces another substance and in doing so becomes oxidised

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3
Q

what is lattice enthalpy

A

the enthalpy change that accompanies the formation of ONE MOLE of an ionic lattice from its gaseous ions under standard conditions

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4
Q

what is standard enthalpy change of formation

A

the enthalpy change that accompanies the formation of ONE MOLE of a compound from its elements in their standard states

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5
Q

what is first ionisation energy

A

the energy change that accompanies the removal of ONE MOLE of electrons from ONE MOLE of gaseous atoms to form gaseous 1+ ions

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6
Q

what’s standard enthalpy change of atomisation

A

the enthalpy change that accompanies the formation of ONE MOLE of gaseous atoms from the element in its standard state

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7
Q

what is first electron affinity

A

the enthalpy change accompanying the formation of ONE MOLE of gaseous 1- ions from gaseous atoms

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8
Q

what are standard conditions

A

1 atm 298K any solutions at 1moldm^-3 concentration

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9
Q

is lattice enthalpy exo or endo

A

exo

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10
Q

is enthalpy change of formation exo or endo

A

varies (usually exo)

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11
Q

is first ionisation energy exo or endo

A

endo

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12
Q

is second ionisation energy exo or endo

A

endo

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13
Q

is standard enthalpy change of atomisation exo or endo

A

endo

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14
Q

is first electron affinity exo or endo

A

exothermic

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15
Q

is second electron affinity exo or endo

A

endo
because the atom is already a negative ion, so doesn’t want another negative electron

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16
Q

why is it impossible to directly measure lattice enthalpy

A

it’s impossible to form 1 mole of an ionic solid from gaseous ions

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17
Q

what does lattice enthalpy depend on and why

A

charge density: stronger charge and smaller ion size
causes greater attraction
so larger lattice enthalpy

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18
Q

what to remember with born haber cycles
(4 points)

A

always include state symbols
exo arrows down, endo arrows up
include electrons (will get used up)
remember to scale via stoichiometry

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19
Q

what is the standard enthalpy change of solution (sol)

A

the enthalpy change that takes place when ONE MOLE of a solute is completely dissolved in water under standard conditions

(s) —> (aq)

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20
Q

what is the standard enthalpy change of hydration (hyd)

A

the enthalpy change that takes place when dissolving ONE MOLE of gaseous jobs in water to form individual aqueous ions

(g) —> (aq)

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21
Q

is standard enthalpy change of solution exo or endo

A

varies

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22
Q

is standard enthalpy change of hydration exo or endo

A

exo

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23
Q

what does the magnitude of enthalpy change of hydration depend on

A

size and charge of ions

causes stronger attraction to water molecules and smaller radii can get closer to water molecules

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24
Q

how can you find lattice enthalpy from hyd and sol

A

hyd is (g) to (aq)
sol backwards is (aq) to (s)

together is (g) to (s) whcih is lattice enthalpy

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25
what is entropy
a measure of the dispersal of energy in a system which is greater the more disordered a system
26
what is entropy unit
JK^-1mol^-1 not kJ!!!!! so convert :)
27
when is entropy higher
when the system becomes more disordered dissolving, in a higher energy state, increased temp
28
what’s the second law of thermodynamics
entropy tends to a maximum (wants to increase)
29
when is entropy 0
at 0K
30
how do you calculate change in enthalpy
S(final) - S(initial)
31
how does delta S get more positive
if a system gets more disordered
32
wording for entropy questions
makes more/less gaseous moles solids are more ordered
33
what does a negative delta G indicate
reaction is spontaneous/feasible
34
what does a positive delta G indicate
reaction isn’t feasible/spontaneous (feasible in reverse direction)
35
what does it mean for a reaction to be spontaneous
if it can do work, generate free energy (G)
36
what does delta G=0 indicate
system is in equilibrium
37
what’s the Gibbs equation
delta G = delta H - T delta S temp in K
38
what can you predict about a reaction where delta H is negative and delta S is positive
spontaneous becuase negative delta G negative minus positive is always negative
39
what can you predict about a reaction where delta H is positive and delta S is negative
not spontaneous, delta G must be positive + - - = +
40
what can you predict about a reaction where delta H is negative and delta S is negative
spontaneous at temps low enough that delta H is bigger than T delta S
41
what can you predict about a reaction where delta H is positive and delta S is positive
spontaneous at temps high enough that T delta S is bigger than delta H
42
what are the limitations of using delta G to predict feasibility
only says if it is thermodynamically possible need to consider kinetics: may need high activation energy rate of reaction may be very slow also reactions with positive delta G can be made to take place
43
what makes a good oxidising agent
easily reduced, good at gaining electrons
44
what makes a good reducing agent
easily oxidised, good at losing electrons
45
steps to balancing redox half equations
work out which element is oxidised or reduced, balance if needed so same amount of this work out oxidation state before and after add electrons to make the oxidation states balance (remember stoichiometry) balance charges of each side with H+ add water molecules to make it all balance
46
how do you combine half equations into overall equation
scale them so that there’s equal amounts of electrons on each side shove them together cancel out
47
how do you approach redox titrations/ what do you need to find
approach as a normal titration question, but instead of acids and bases it’s oxidised and reduced species
48
what can manganate be used to oxidise
Fe^2+ to Fe^3+
49
manganate colour change when used in redox titration
MnO4^- —> Mn^2+ purple —> colourless +7 —> +2
50
what are the conditions for iron manganate redox titrations and why
acidic, sulphuric acid usually becuase it is in the presence of H+ ions (from the half equations)
51
how can you know end point has been reached in iron manganate redox titrations
when excess MnO4^- ions are present (all the Fe2+ has reacted) so a faint pink colour appears (due to Mn oxidation number 7+ is purple)
52
what can iodine be used to oxidise in a redox titration
thiosulphate ions S2O3^2-
53
what is iodines colour change when used in redox titrations
I2 —> I^- blue-black —> colourless 0 —> -1
54
what conditions do iodine thiosulphate redox titrations need and why
need to be in the presence of starch for iodines colour change to occur
55
what is the end point of iodine thiosulphate redox titrations
when all the blue-black colour disappears, so all the iodine has oxidised the thiosulphate ions
56
what’s the overall equation between thiosulphate ions and iodine
2S2O3^2- + I2 —> S4O6^-2 + 2I^-
57
what is the standard electrode potential of a half cell
the e.m.f. of a half cell compared with a standard hydrogen half cell, measured at 298K with solutions at 1M conc and a gas pressure of 1 atm
58
when drawing a cell, what should you include
salt bridge between beakers, TOUCHING SOLUTIONS electrodes, labelled solutions, making sure to write standard conditions if applicable, electrodes connected by a wire and a voltmeter at the top
59
what happens in the salt bridge
ions travel through it
60
what happens in the wire of a cell
electrons travel through it
61
what happens at the positive electrode
oxidation, donates electrons into the solution
62
what happens at the negative electrode
reduction, accepts electrons from the solution
63
how are half equations of half cells written
as reduction
64
how would you make a half cell out of a metal in contact with a solution of its ions
electrode made of the metal, solution contains 1 moldm^-3 of the ION
65
what must you be careful of with concentrations of solutions in half cells for standard conditions
that it’s 1M of the ION not the whole molecule, eg if you want H+ ions, you would use 0.5 M of H2SO4 to get 1M H+
66
how would you make a half cell out of gases
use a platinum (inert but conductive) electrode and have an upside down test tube (that goes under the solution line) with the gas at 1 atm and 298 K being fed in
67
how would you make a half cell out of solutions if ions in two different oxidation states
platinum electrode touching solution with 1M of each ion
68
i’m terms of electrode potentials, which are the best oxidising agents and why
highest electrode potential elements are the best oxidising agents because they are the most easily reduced
69
what to be careful with when saying the best reducingagent
won’t usually be an ion, it will be the product of the reduction equation, as it is the thing that can lose electrons (oxidise)
70
how do you combine half cell potentials to find out cell potentials
the more positive electrode potential will stay as reduction and will reverse the one with a less positive value into being oxidised
71
how do you get the overall cell equation
combine the two half equations as usual (remembering to balance the electrons)
72
how do you work out overall cell potential from electrode potentials
the one being reduced (more positive) - the one being oxidised (less positive)
73
what is potential measured in
V
74
what’s the trend in the best oxidising agents (most positive electrode potentials)
more electronegative, the more positive electrode potential value
75
how can you use equilibrium to discuss redox equations and electrode potentials
the half equations are reversible, so the position of equilibrium can move to oppose changes to conditions, which will affect electrode potential values (eg if backward reaction is favoured, it is better at getting oxidised, is a better reducing agent, and has a lower electrode potential)
76
how can you predict feasibility using electrode potentials and cell potential
if the electrode potential is positive the reaction of feasible
77
limitations of predicting feasibility using electrode potentials
if not at standard conditions electrode potentials change (use le chateliers principle to predict) the predictions fail to consider kinetics (rate and activation energy)
78
what do non rechargeable cells do
provide electrical energy until the chemicals run ouy
79
what do rechargeable cells do
provide electrical energy, but the reaction can be reversed during recharging
80
what does a fuel cell do
the cell reaction uses external supplies of a fuel and oxidant which need to be continuously supplied for the cell to provide electrical energy
81
how do fuel cells work
use energy from the reaction of a fuel with oxygen to create a voltage the reactants flow in and products flow out while the electrolyte stays in the cell can operate continuously as long as the fuel and oxygen continue to flow into the cell
82
what is the cell potential for every hydrogen fuel cell
1.23 V
83
Is a reaction feasible when delta G=0
Yes

chemistry year 13 (6 decks)

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