physical chem and transition elements Flashcards
what does enthalpy of formation mean?
the enthalpy change when 1 mole of a compound is formed from its element under standard conditions
what does ionisation enthalpy mean?
the amount of energy required to remove an electron from a gaseous atom of an element to from a gaseous ion under standard conditions
what does enthalpy change of atomisation mean?
the enthalpy change when 1 mole of gaseous atoms is formed from its element under standard conditions
what does bond enthalpy mean?
the amount of energy required to break 1 mole of a specific covalent bond in the gas phase
what does lattice energy mean?
the enthalpy change when 1 mole of ionic compound is formed from its gaseous ions under standard conditions
what factors affect lattice enthalpy?
ionic radius
as it increases, attraction between ions decreases so lattice enthalpy becomes less exothermic and melting point decreases
ionic charge
as it increases, attraction between ions increases so lattice enthalpy becomes more exothermic and melting point increases
what does enthalpy change of solution mean?
the enthalpy change that takes place when one mole of a compound is completely dissolved in water under standard conditions
what does standard enthalpy change of hydration mean?
when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions
what does the entropy (S) of a given system mean?
the number of possible arrangements of the particles and energy in a given system
list the states in ascending order of entropy
solid, liquid, gas
what is the equation for change in entropy (S)
Σ S products - Σ S reactants
what is the Gibbs equation used to calculate?
if a reaction is feasible or not
what is the Gibbs equation?
ΔGꝋ = ΔHreactionꝋ - TΔSsystemꝋ
ΔGꝋ = ΣΔGproductsꝋ - ΣΔGreactantsꝋ
what does a negative ΔGꝋ value mean?
the reaction is feasible
what does a positive ΔGꝋ value mean?
the reaction is not feasible
what is ΔH in an exothermic reaction?
negative
what is ΔH in an endo reaction?
positive
what are the limitations of using ΔG?
can only be used under standard conditions
doesn’t take into account rate of reaction
some reactions are feasible but not kinetically feasible cos too slow
what is an oxidising agent?
oxidise another atom/ ion by causing it to lose electrons
gets reduced- gains electrons
so oxidation number decreases
what is a reducing agent?
reduces another atom/ ion by causing it to gain electrons
gets oxidised- loses electrons
so oxidation number increases
explain potassium manganate (VII) titrations
manganate(VII) is oxidising agent
reduced to Mn2+
iron is reducing agent
oxidised to Fe3+
reaction mixture must be acidified to excess dilute sulphuric acid added to Fe3+ before reaction
potassium permanganate starts purple
Mn2+ is pale pink but appears colourless cos of low conc
when all Fe2+ reacted with Mn7+, pale pink solution due to excess Mn7+
why is dilute sulphuric acid suitable for potassium manganate (VII) titrations?
does not oxidise under the conditions
does not react with manganate (VII)
why is HCl not suitable for potassium manganate (VII) titrations?
can be oxidised to Cl by manganate (VII)
why is nitric acid not suitable for potassium manganate (VII) titrations?
oxidising agent
may oxidise substances
why is ethanoic acid not suitable for potassium manganate (VII) titrations?
weak acid
insufficient concentration of H+ ions
why is conc sulphuric acid not suitable for potassium manganate (VII) titrations?
may oxidise substances
explain iodine thiosulfate titrations
light brown/ yellow of iodine turns paler when converted to colourless iodide ions
when solution is a straw colour, starch is added
turns blue/black until all iodine reacts, then colour disappears
what can iodine thiosulfate titrations be used for determining?
amount of chlorate(I) in bleach
amount of Cu2+ in copper(II) compounds
copper content of alloys
what can potassium manganate titrations be used for determining?
percentage purity of iron supplements
formula of a sample of hydrated ethanedioic acid
what does the position of equilibrium and electrode potential depend on?
temp
pressure of gases
conc of reagents
what conditions are used when comparing electrode potentials?
standard
ion conc of 1moldm-3
298K
100kPa
what is used to take standard electrode potential measurements?
high resistance voltmeter
so no current flows
and max pd achieved
what is a standard hydrogen electrode?
contains hydrogen gas in equilibrium with H+ ions of concentration 1moldm-3 at 100kPa and an inert platinum electrode
0.00V
what is standard electrode potential?
potential difference produced when a standard half cell is connected to a standard hydrogen cell under standard conditions
which half cell is more likely to get reduced?
the more positive one
which half cell is less likely to get reduced?
the more negative one
why is platinum wire used as an electrode?
inert
what are the units of rate of reaction?
mol dm-3 s-1
which step is the rate determining step?
the slowest step in the reaction
what are transition elements?
elements w an incomplete d sub shell that can from at least 1 stable ion w an incomplete d sub shell
what are the properties of transition elements?
forming coloured compounds
used as catalysts
forming complex ions
variable oxidation states
test for CO3^2-
add dilute acid
effervescence
test gas w limewater
confirms its CO2
test for SO4^2-
acidified BaCl2
white ppt of BaSO4
test for halide ions
add acidified AgNO3
AgCl white ppt- dissolves in dilute ammonia
AgBr cream- dissolves in conc
AgI yellow- insoluble
test for ammonium ions
add OH-
ammonia gas forms
which turns damp red litmus paper blue
confirming presence of NH4+ in og solution
ligand
a molecule or ion that can donate an electron pair to a transition metal ion
coordination number
the total number of dative covalent bonds formed between the central metal ion and its ligands
complex ions
transition metal ion bonded to ligands by dative covalent bonds
coordinate/ dative covalent bonds
sharing of a pair of electrons, with both electrons coming from the same atom
monodentate ligand
ligand that is able to donate 1 pair of electrons to the central metal ion
bidentate ligand
ligand that is able to donate 2 pairs of electrons to the central metal ion
examples of monodentate ligands
H2O
OH-
NH3
CN-
Cl-
examples of bidentate ligands
1,2- diaminoethane
ethandioate
how many bonds in octahedral shape and what is the bond angle
6
90º
how many bonds in tetrahedral shape and what is the bond angle
4
109.5º
how many bonds in square planar shape and what is the bond angle
4
90º
what are ligand substitution reactions?
when one ligand in a complex is replaced by another
to form a more stable complex
ligands can be partially or entirely substituted
when do transition element complexes show cis stereoisomerism?
when 2 different ligands are next to each other
when do transition element complexes show trans stereoisomerism?
when 2 different ligands are opposite to each other
what shape transition element complexes show optical isomerism?
octahedral complexes with bidentate ligands
what are optical isomers?
2 forms are non superimposable mirror images
no plane of symmetry
one image cannot be placed directly on top of the other
how does cisplatin work to treat cancer?
passes thru cell membrane and undergoes ligand exchange where cl is replaced by water
N is a better ligand than water so forms dative covalent bonds w cisplatin
cisplatin distorts shape of DNA and prevents it from replicating
why is hair loss a side effect of cancer treatment?
cisplatin binds to other quickly replicating cells eg hair follicles
how does haemoglobin transport oxygen?
haem molecule is a complex w a central Fe(ll)
O2 form a dative covalent bond w Fe(ll) which enables O2 to be transported around body in blood
O2 bond weakly to Fe(ll)
weak bond allows them to break off easily and be transported into cells
how does CO bond to haemoglobin?
CO is a better ligand than O2 so binds strongly and irreversibly to Fe(ll)
preventing O2 from being carried to cells
what is anaemia?
lack of haemoglobin due to blood loss or iron deficiency
[Cu(H2O)6]2+ (aq) colour
pale blue
CoCl2.6H2O (s) plus water and excess HCl
CoCl4^2-
blue
oxidation of Cr3+ with hot alkaline H2O2
CrO4^2-
yellow
NaOH drowse to Fe3+(aq)
Fe(OH)3 (s)
orange brown ppt
NH3 dropwise to Cu2+(aq)
Cu(OH)2(s)
pale blue ppt
[Cr(H2O)6]3+
pale purple
Due to impurities, it is common for Cr(III) to appear green in solution
[Mn(H2O)6]2+
pale pink
MnO4–/Fe2+ > Mn2+/Fe3+
purple (MnO4–) to pale pink (Mn2+) (in titrations, so dilute that it is practically colourless)
excess NH3 to Cu2+(aq)
[Cu(NH3)4(H2O)2]2+
dark blue
NH3 dropwise to Cr 3+(aq)
Cr(OH)3(s)
dark green ppt
NaOH dropwise to Mn2+(aq)
Mn(OH)2(s)
pale brown ppt
excess HCl to Cu2+(aq)
CuCl4^2–
yellow
excess NH3 to Cr2+(aq)
[Cr(NH3)6]3+
purple
[Fe(H2O)6]2+
pale green
I–/Fe3+ > I2/Fe2+
orange brown (Fe3+) to brown (I2)
reduction of Cu2+ with I–
white precpitate (CuI) and brown I2
excess OH– to Cr(OH)3(s)
[Cr(OH)6]3–
dark green
NaOH dropwise to Fe2+(aq)
Fe(OH)2(s)
dark green ppt
Disproportionation of Cu+
brown solid (Cu) and blue solution (CuSO4)
Cr2O7^2–
orange
[Fe(H2O)6]3+
yellow
units for Delta G
kJmol-1
or
Jmol-1
is enthalpy change of formation endo or exo
exo
is enthalpy change of atomisation endo or exo
endo
is 1st e- affinity endo or exo
exo
is 2nd e- affinity endo or exo
endo
why is 2nd e- affinity endo
energy needed to add an e- onto a neg ion
repulsion between e- and neg ion
factors that effect enthalpy change of hydration
charge:
larger charge, larger enthalpy change of hydration
size:
smaller size, larger enthalpy change of hydration
thing to remember when calculating things from born haber cycles
go w arrow: keep sign same
go against arrow: change sign
enthalpy change of hydration reaction
lattice enthalpy
+
enthalpy change of solution
how to find temp at which feasibility changes
delta H / delta S
what elements are d block but not transition elements
Sc
Zn
charge of bidentate ligand 1,2- diaminoethane
neutral
charge of bidentate ligand ethanedioate
2-
what shape do complexes w coordination number 6 always make
octahedral
what shape do complexes w coordination number 4 make
tetrahedral
square planar
How to calculate mole fraction
Equilibrium moles of gas
/
Total moles
How to calculate partial pressure
Mole fraction x total pressure
What is the position of equilibrium if Kc = 1
Half way between reactants and products
What is the position of equilibrium if Kc > 1
Right
More products at equilibrium
What is the position of equilibrium if Kc < 1
Left
More reactants at equilibrium
What condition change affects Kc and Kp
Only temperature
What is the effect on Kc and Kp of increasing the temperature for a reaction which is forward exothermic
Shifts equilibrium to the left
Kc and Kp decrease
What is the effect on Kc and Kp of increasing the temperature for a reaction which is forward endothermic
Shifts equilibrium to right
Kc and Kp both increase
What is a bronsted acid
Species that can donate a proton
What is a brønsted base
Species that can accept a proton
What are conjugate acid-base pairs
2 species that are different from each other by an H+ ion
What is a monobasic acid
Contains 1 ionisable H atom
What is a bronsted acid
Especies chat Caín
Monobasic acid examples
HCN
HCl
HNO3
Dibasic acid example
H2SO4
Tribasic acid example
H3PO4
What is a weak acid
Parcial dissociates in aqueos solution
Weak acid example
Ethanoic
Where is the position of equilibrium for weak acids
Left
more HA molecules than H+ and A-
What is the acid dissociation constant ka
[H+][A-]
/
[HA]
Acid dissociation constant ka units
mol dm -3
What does a higher ka value mean
More dissociated, stronger acid
pH equation
-log [H+]
H+ ion concentration equation
10 ^ -pH
Assumption made when using ka
[H+] = [A-] at equilibrium
Initial [HA] = equilibrium [HA]
