definitions and model answers Flashcards
ligand substitution
a reaction in which one ligand in a complex ion is replaced by another ligand
How to store hydrogen
liquid stored under pressure
adsorbed on the surface of a solid
absorbed within a solid
What is the different between electrochemical and fuel cells?
fuel cells convert energy from the reaction of a fuel with oxygen into electrical energy
electrochemical cells generate electrical energy via the electron transfer between half cells of different electrode potential
bidentate ligand
ions or molecules, which donate 2 lone pairs or electrons to form 2 coordinate bonds to a central metal ion
redox reaction
a reaction in which both reduction and oxidation takes place
coordinate bond
a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only
Fuel cell
A fuel cell converts the energy from a reaction of a fuel with oxygen into a voltage/electrical energy
precipitation reaction
the formation of a solid from a solution during a chemical reaction. precipitates are often formed when two aqueous solutions are mixed together
complex ion
a central transition metal ion that is bonded to one or more ligands by coordinate bonds
write an equation for the addition of excess concentrated HCL to a solution of copper sulphate
[Cu(H2O)6] 2+ + 4Cl- [CuCl4] 2- + 6H2O
blue solution —-> yellow/green solution
reduction
gain of electrons and a decrease in oxidation number
reduction
Gain of electrons or a decrease in oxidation number
stability constant kstab
the equilibrium constant for an equilibrium existing between a transition metal ion surrounded by water ligands and the complex formed when the same ion has undergone a ligand substitution
why are M 3+ hexaaqua ions more acidic than M 2+ hexaaqua ions?
the charge density is greater for M 3+ than M 2+
therefore the M 3+ has a greater attraction for H2O ligands
this makes the O-H bonds more polar and weaker
meaning H+ ions are released more easily
write an equation for the reaction of sodium hydroxide with a solution of copper(II) sulphate and give the colour change
[Cu(H20)6] 2+ + 2OH- [Cu(H2O)4(OH)2] + 2H2O
blue solution —-> blue precipitate
write an equation for the reaction of sodium hydroxide with a solution of iron (II) sulphate and give the colour change
[Fe(H20)6] 2+ + 2OH- [Fe(H2O)4(OH)2] + 2H2O
green solution —-> dirty green precipitate
stereoisomers
species with the same structural formula but with a different arrangement of atoms in space
write an equation for the reaction of sodium hydroxide with a solution of iron (III) sulphate and give the colour change
[Fe(H20)6] 3+ + 3OH- [Fe(H2O)3(OH)3] + 3H2O
orange yellow solution —-> brown precipitate
write an equation for the addition of excess concentrated HCL to a solution of cobalt chloride
[Co(H2O)6] 2+ + 4Cl- [CoCl4] 2- + 6H2O
Pink solution —-> blue solution
Exothermic and the temperature is decreasing…
i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?
i) increase
ii) increase
iii) decrease
iv) moves right
write an equation for the addition of excess ammonia to a solution of copper sulphate
[Cu(H2O)6] 2+ + 4NH3 [Cu(NH3)4(H2O)2] 2+ + 4H2O
blue solution —-> deep blue solution
How does haemoglobin work
in haemoglobin, oxygen bonds to the Fe2+ ion
when required the oxygen is substituted/ released
On a concentration rate graph. what is first order?
A straight line with a constant slope
must go through the origin
rate is proportional to concentration
gradient=rate constant (k)
Equilibrium law
For the equilibrium
aA +bB cC +dD
Kc = [C]^c [D]^d
-----------------
[A]^a [B]^boxidation
loss of electron and an increase in oxidation number
Rate of reaction
The change in the concentration of reactants or products over time
write an equation for the reaction of sodium hydroxide with a solution of cobalt(II) chloride and give the colour changes
[Co(H20)6] 2+ + 2OH- [Co(H2O)4(OH)2] + 2H2O
pink solution —–> blue/pink precipitate
Order of reaction
The power to which a concentration is raised in the rate equation
Half life
The time taken for the concentration of the reactants to drop by half
What are the units of rate?
mol dm-3 s-1
units of concentration
moldm-3
On a concentration time graph, what is zero order?
A straight line with a constant slope
On a concentration time graph, what is first order?
Downwardly sloping curve with a constant half life
coordination number
the total number of coordinate bonds formed between the central metal ion and any ligand
On a concentration time graph, what is second order?
Steeper downwardly sloping curve but levels out quicker
What changes the value of Kc?
temperature
ligand
atoms, ions or molecules that can donate a lone pair of electrons to form coordinate bonds to a central transition metal ion
the reason CO is a danger to us
complexes of haemoglobin and CO have greater Kstab than complexes of haemoglobin and O2. this is because the coordinate bond with CO is stronger than with O2
Dynamic equilibrium
The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction
d-block element
an element where the d sub-shell is the highest energy sub-shell that is occupied
oxidation number
loss of electrons or an increase in oxidation number
Homogeneous equilibrium
An equilibrium in which all the species making up the reactants and products are in the same physical state
Le Chatliers principle
When a system in dynamic equilibrium is subjected to a change, the system readjusts itself to minimise the effect of the change and to restore equilibrium
If Kc=1
The position of equilibrium is halfway between the reactants and products
Enthalpy, ∆H
The heat content that is stored in a chemical system
On a concentration rate graph, what is second order?
An upward sloping curve
Changing the concentration and pressure - what happens to Kc
Kc does not change
The system is no longer in equilibrium
State the effect of the change on values in the Kc expression (e.g. the increase in pressure increases the terms on the bottom of the Kc expression more than the terms on top)
State how the terms of the Kc expression alter to oppose the change (e.g. The top of the Kc expression increases and the bottom decreases until Kc is reached/restored)
Equilibrium will shift left/right to restore Kc
Ka
for the acid HA
ka = [H+(aq)][A-(aq)]
———————-
[HA(aq)]
If Kc<1
The position of equilibrium is on the left hand side (reactants) of the reaction
Rate determining step
Defined as the slowest step to a reaction
Endothermic and the temperature is decreasing…
i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?
i) decrease
ii) decrease
iii) increase
iv) Moves left
What is the equation of the rate?
rate = k [A][B]^2
Heterogeneous equilibrium
An equilibrium in which the species making up the reactants and products are in different physical states
Describe the change in equilibrium position due to an decrease in pressure
Equilibrium moves to the left/right
As there are more gaseous moles
Bronsted Lowry acid
A species that is a proton donor
Bronsted Lowry base
A species that is a proton acceptor
Alkali
A type of base that dissolves in water to form hydroxide OH- (aq) ions
Second ionisation energy
the energy required to remove one electron from each ion in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions
Strong acid
An acid that completely dissociates in solution
Monoprotic acid
An acid that releases one H+ ion per acid molecule
Diprotic acid
An acid that releases two H+ ions per acid molecule
Weak acid
An acid that partially dissociates in solution
Exothermic and the temperature is increasing…
i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?
i) decrease
ii) decrease
iii) increase
iv) moves left
pKa
pKa = -log(ka)
Standard enthalpy on neutralisation ∆Hneut®
The energy change that accompanies the neutralisation of an aqueous acids by an aqueous base to form one mole of H2O (l) under standard conditions
pH
pH = -log[H+(aq)]
Conjugate acid
A species formed when proton is added to a base
On a concentration rate graph, what is zero order?
A straight line horizontal to the x axis
Rate is independent of concentration
If Kc>1
The position of equilibrium is on the right hand side (products) of the reaction
Conjugate base
A species formed when a proton is added to an acid
Buffer solution
A system that minimises pH changes on addition of small amounts of an acid or a base
How does a buffer solution work?
The workings of a \_\_\_\_\_\_\_1\_\_\_\_\_\_\_\_ acid buffer can be explained by \_\_\_\_\_\_1\_\_\_\_\_\_\_ \_\_\_\_\_\_\_2\_\_\_\_\_\_ + H+ Added acid reacts with \_\_\_\_\_\_\_2\_\_\_\_\_\_ Equilibrium shifts to the left Added alkali/base reacts with H+ Equilibrium shifts to the right
What is the equivalence point?
When the volume of one solution has reacted exactly with a known volume of another
Describe the change in equilibrium position due to an increase in pressure
Equilibrium moves to the left/right
As there are fewer gaseous moles
Plan an experiment that a student could carry out to measure the enthalpy change of neutralisation
Acid and alkali mixed
amounts of acid and alkali stated
Temp taken at start and finish
Energy - q=mc∆T and the meaning of m, c, ∆T
∆H = -energy change
If temp inc, ∆H=-ve , if temp dec, ∆H=+ve
First electron affinity
The enthalpy change that accompanies the addition of one electron to each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Standard enthalpy change of reaction ∆Hr®
The enthalpy change that accompanies a reaction in the molar quantities expresses in a chemical equation under standard conditions, all reactants and products being in their standard states
Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard condition
Standard enthalpy of atomisation
The enthalpy change that takes place when one mole of gaseous atoms form from the element in its standard states
transition metal
a d-blck element that forms one or more table ions with a partially filled d sub-shell
First ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions
Exothermic reaction
A reaction in which the enthalpy of products is smaller than the enthalpy of the reactants, resulting in heat loss to the surroundings. ∆H = -ve
A suitable indicator must
Change over the vertical section of the curve where there is a large change in pH for the addition of a very small volume
Standard enthalpy change of hydration
The enthalpy change that takes place when one mole of isolated gaseous ions is dissolved in water forming one mole of aqueous ions under standard conditions
Second electron affinity
The enthalpy change that accompanies the addition of one electron to each ion in one mole of gaseous 1- ions to from one mole of gaseous 2- ions
Standard enthalpy change of solution
The enthalpy change that takes place when one mole of a compound is completely dissolves in water under standard conditions
Lattice dissociation enthalpy
The enthalpy when one mole of an ionic lattice dissociates into isolated gaseous ions
Lattice formation enthalpy
The enthalpy change when one mole of an ionic crystal lattice is formed from its isolated gaseous ions
Triprotic acid
An acid that release three H+ ions per acid molecule
Endothermic and the temperature is increasing…
i) What is the effect on Kc?
ii) What is the effect on product concentration?
iii) What is the effect on reactant concentration?
iv) What is the direction of change of equilibrium?
i) increase
ii) increase
iii) decrease
iv) moves right
Enthalpy
The heat content that is stored in a chemical system
Entropy
The quantitative measure of the degree of disorder in a system
Standard entropy change of reaction ∆S®
The entropy change that accompanies a reaction in the molar quantities expresses in a chemical equation under standard conditions, all reactants and products being in their standard states
What symbol is associated with entropy?
S
Standard enthalpy of formation ∆Hf®
The enthalpy change that takes place when one mole of a compound in its standard state is formed from its constituents elements in their standard state under standard conditions
Units of the free energy calculation
∆G = ∆H - T∆S
KJ-1 mol-1 = KJmol-1 - K(JK-1mol-1)
When does entropy increase?
Solid melts Liquid boils Solid dissolves in water the number of gas molecules increases the temperature increases
How do you calculate entropy change?
∆S = ∑S® products - ∑S® reactants
What is the symbol for free energy change
∆G
If ∆H = -ve
∆S = +ve
i) what will ∆G be?
ii) Will the reaction be feasible?
i) always -ve
ii) reaction is feasible
If ∆H = +ve
∆S = -ve
i) what will ∆G be?
ii) Will the reaction be feasible?
i) Always +ve
ii) reaction is never feasible
Ionic product of water, Kw
Kw = [H+][OH-] = 1.00 x 10 ^-14 mol2 dm-6 at 25˚C
If ∆H = +ve
∆S = +ve
i) what will ∆G be?
ii) Will the reaction be feasible?
i) -ve at high temperature
ii) Reaction feasible ay high temperature
If ∆G ≤ 0
spontaneous reaction
Free energy change ∆G
The balance between enthalpy, entropy and temperature for a process
∆G = ∆H - T∆S
A process can take place spontaneously when ∆G<0
If ∆G ≥0
non-spontaneous reaction
If ∆G = 0
The system is in equilibrium
Redox reaction
A reaction in which both reduction and oxidation takes place
Oxidation number
A measure of the number of electrons that an atom uses to bond with atoms of another element. Oxidation numbers are derived from a set of rules
Reducing agent
A reagent that reduces (adds electrons to) another species
Oxidising agent
A reagent that oxidises (takes electrons from) another species
Why is platinum electrodes used?
The conduct electricity- allows electrons to pass into and out of the cell
They are inert so take no part in the reaction
Why might +ve cell potential reactions not happen?
The activation energy is too high
There aren’t standard conditions e.g. concentrations are not 1 moldm-3 …
Advantages of fuel cells
Eliminates pollution causes by burning fossil fuels - the only by product is water
Eliminates greenhouse gases if the hydrogen used comes from electrolysis of water
eliminates economic dependence on politically unstable countries for fossil fuels
Have a higher efficiency than diesel or gas engines
Most operate silently compared to internal combustion engines
Some have low heat transmission - ideal for military applications
operating times are much longer than with batteries
maintenance is simple since there are few moving parts in the system
Alternative cells use methanol as the fuel - advantages
liquid fuels are easier to store
methanol can be generated from biomass
Advantages of fuel cell vehicles
produce less pollution from exhaust gases (no NOx, CO, unburnt hydrocarbons)
produce less CO2
more efficient
Limited supplies of fossil fuels may causes us to move to a hydrogen economy- however…
a greater acceptance by the public and politicians is necessary
handling and maintenance of hydrogen systems must be safe
improvements to hydrogen manufacturing must be made
Standard electrode potential
The e.m.f. (electromotive force) of a half cell compared with a standard hydrogen half cell, measured at 298K with solution concentration of 1 moldm-3 and a gas pressure of 100kPa (1 atmosphere)
If ∆H = -ve
∆S = -ve
i) what will ∆G be?
ii) Will the reaction be feasible?
i) -ve at low temperatures
ii) Reaction feasible at low temperatures
Disadvantages of fuel cells
production, transportation, distribution and storage of hydrogen is difficult
reforming is technically challenging and not environmentally friendly
refuelling and starting times of fuel cell vehicles (FCV’s) are longer
driving range cars is shorter than in a tradition vehicle
fuel cells are generally slightly bigger than comparable batteries or engines
currently expensive to produce, since most units are hand made
some use expensive materials
the technology is not yet fully developed and few products are available
What is entropy usually measured in?
joules
Endothermic reaction
A reaction in which the enthalpy of the products is greater than the enthalpy of the reactants resulting in heat being taken in from the surroundings, ∆H = +ve
disadvantages of hydrogen based fuel cells
storage of hydrogen - safety considerations
transportation of hydrogen - low density so expensive to deliver
feasibility of liquified hydrogen under pressure - safety considerations
limited life adsorbed/absorber - economic considerations
limited life cycle of cell - economical considerations
high production costs - economic considerations
use toxic chemicals in cell production - environmental considerations
