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Chemistry Unit 5 > definitions and model answers > Flashcards

definitions and model answers Flashcards

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0
Q

ligand substitution

A

a reaction in which one ligand in a complex ion is replaced by another ligand

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1
Q

How to store hydrogen

A

liquid stored under pressure
adsorbed on the surface of a solid
absorbed within a solid

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2
Q

What is the different between electrochemical and fuel cells?

A

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

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3
Q

bidentate ligand

A

ions or molecules, which donate 2 lone pairs or electrons to form 2 coordinate bonds to a central metal ion

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4
Q

redox reaction

A

a reaction in which both reduction and oxidation takes place

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5
Q

coordinate bond

A

a shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only

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6
Q

Fuel cell

A

A fuel cell converts the energy from a reaction of a fuel with oxygen into a voltage/electrical energy

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7
Q

precipitation reaction

A

the formation of a solid from a solution during a chemical reaction. precipitates are often formed when two aqueous solutions are mixed together

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8
Q

complex ion

A

a central transition metal ion that is bonded to one or more ligands by coordinate bonds

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10
Q

write an equation for the addition of excess concentrated HCL to a solution of copper sulphate

A

[Cu(H2O)6] 2+ + 4Cl- [CuCl4] 2- + 6H2O

blue solution —-> yellow/green solution

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12
Q

reduction

A

gain of electrons and a decrease in oxidation number

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13
Q

reduction

A

Gain of electrons or a decrease in oxidation number

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14
Q

stability constant kstab

A

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

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15
Q

why are M 3+ hexaaqua ions more acidic than M 2+ hexaaqua ions?

A

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

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16
Q

write an equation for the reaction of sodium hydroxide with a solution of copper(II) sulphate and give the colour change

A

[Cu(H20)6] 2+ + 2OH- [Cu(H2O)4(OH)2] + 2H2O

blue solution —-> blue precipitate

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17
Q

write an equation for the reaction of sodium hydroxide with a solution of iron (II) sulphate and give the colour change

A

[Fe(H20)6] 2+ + 2OH- [Fe(H2O)4(OH)2] + 2H2O

green solution —-> dirty green precipitate

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18
Q

stereoisomers

A

species with the same structural formula but with a different arrangement of atoms in space

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18
Q

write an equation for the reaction of sodium hydroxide with a solution of iron (III) sulphate and give the colour change

A

[Fe(H20)6] 3+ + 3OH- [Fe(H2O)3(OH)3] + 3H2O

orange yellow solution —-> brown precipitate

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19
Q

write an equation for the addition of excess concentrated HCL to a solution of cobalt chloride

A

[Co(H2O)6] 2+ + 4Cl- [CoCl4] 2- + 6H2O

Pink solution —-> blue solution

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20
Q

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?

A

i) increase
ii) increase
iii) decrease
iv) moves right

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22
Q

write an equation for the addition of excess ammonia to a solution of copper sulphate

A

[Cu(H2O)6] 2+ + 4NH3 [Cu(NH3)4(H2O)2] 2+ + 4H2O

blue solution —-> deep blue solution

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23
Q

How does haemoglobin work

A

in haemoglobin, oxygen bonds to the Fe2+ ion

when required the oxygen is substituted/ released

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24
Q

On a concentration rate graph. what is first order?

A

A straight line with a constant slope
must go through the origin
rate is proportional to concentration
gradient=rate constant (k)

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25
Q

Equilibrium law

A 
For the equilibrium 
aA +bB  cC +dD
Kc = [C]^c [D]^d
        -----------------
         [A]^a [B]^b
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26
oxidation
loss of electron and an increase in oxidation number
27
Rate of reaction
The change in the concentration of reactants or products over time
28
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
29
Order of reaction
The power to which a concentration is raised in the rate equation
30
Half life
The time taken for the concentration of the reactants to drop by half
31
What are the units of rate?
mol dm-3 s-1
32
units of concentration
moldm-3
33
On a concentration time graph, what is zero order?
A straight line with a constant slope
34
On a concentration time graph, what is first order?
Downwardly sloping curve with a constant half life
35
coordination number
the total number of coordinate bonds formed between the central metal ion and any ligand
36
On a concentration time graph, what is second order?
Steeper downwardly sloping curve but levels out quicker
37
What changes the value of Kc?
temperature
38
ligand
atoms, ions or molecules that can donate a lone pair of electrons to form coordinate bonds to a central transition metal ion
39
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
40
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
41
d-block element
an element where the d sub-shell is the highest energy sub-shell that is occupied
41
oxidation number
loss of electrons or an increase in oxidation number
44
Homogeneous equilibrium
An equilibrium in which all the species making up the reactants and products are in the same physical state
45
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
46
If Kc=1
The position of equilibrium is halfway between the reactants and products
47
Enthalpy, ∆H
The heat content that is stored in a chemical system
48
On a concentration rate graph, what is second order?
An upward sloping curve
48
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
49
Ka
for the acid HA ka = [H+(aq)][A-(aq)] ---------------------- [HA(aq)]
50
If Kc<1
The position of equilibrium is on the left hand side (reactants) of the reaction
51
Rate determining step
Defined as the slowest step to a reaction
52
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
53
What is the equation of the rate?
rate = k [A][B]^2
54
Heterogeneous equilibrium
An equilibrium in which the species making up the reactants and products are in different physical states
55
Describe the change in equilibrium position due to an decrease in pressure
Equilibrium moves to the left/right | As there are more gaseous moles
57
Bronsted Lowry acid
A species that is a proton donor
58
Bronsted Lowry base
A species that is a proton acceptor
59
Alkali
A type of base that dissolves in water to form hydroxide OH- (aq) ions
60
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
61
Strong acid
An acid that completely dissociates in solution
62
Monoprotic acid
An acid that releases one H+ ion per acid molecule
62
Diprotic acid
An acid that releases two H+ ions per acid molecule
63
Weak acid
An acid that partially dissociates in solution
64
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
67
pKa
pKa = -log(ka)
68
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
69
pH
pH = -log[H+(aq)]
70
Conjugate acid
A species formed when proton is added to a base
71
On a concentration rate graph, what is zero order?
A straight line horizontal to the x axis | Rate is independent of concentration
71
If Kc>1
The position of equilibrium is on the right hand side (products) of the reaction
71
Conjugate base
A species formed when a proton is added to an acid
71
Buffer solution
A system that minimises pH changes on addition of small amounts of an acid or a base
72
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 ```
72
What is the equivalence point?
When the volume of one solution has reacted exactly with a known volume of another
73
Describe the change in equilibrium position due to an increase in pressure
Equilibrium moves to the left/right | As there are fewer gaseous moles
74
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
76
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
79
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
80
Lattice enthalpy
The enthalpy change that accompanies the formation of one mole of an ionic compound from its gaseous ions under standard condition
81
Standard enthalpy of atomisation
The enthalpy change that takes place when one mole of gaseous atoms form from the element in its standard states
82
transition metal
a d-blck element that forms one or more table ions with a partially filled d sub-shell
83
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
84
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
85
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
85
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
86
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
87
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
88
Lattice dissociation enthalpy
The enthalpy when one mole of an ionic lattice dissociates into isolated gaseous ions
89
Lattice formation enthalpy
The enthalpy change when one mole of an ionic crystal lattice is formed from its isolated gaseous ions
90
Triprotic acid
An acid that release three H+ ions per acid molecule
91
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
92
Enthalpy
The heat content that is stored in a chemical system
93
Entropy
The quantitative measure of the degree of disorder in a system
94
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
95
What symbol is associated with entropy?
S
96
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
97
Units of the free energy calculation
∆G = ∆H - T∆S | KJ-1 mol-1 = KJmol-1 - K(JK-1mol-1)
98
When does entropy increase?
``` Solid melts Liquid boils Solid dissolves in water the number of gas molecules increases the temperature increases ```
99
How do you calculate entropy change?
∆S = ∑S® products - ∑S® reactants
100
What is the symbol for free energy change
∆G
101
If ∆H = -ve ∆S = +ve i) what will ∆G be? ii) Will the reaction be feasible?
i) always -ve | ii) reaction is feasible
102
If ∆H = +ve ∆S = -ve i) what will ∆G be? ii) Will the reaction be feasible?
i) Always +ve | ii) reaction is never feasible
103
Ionic product of water, Kw
Kw = [H+][OH-] = 1.00 x 10 ^-14 mol2 dm-6 at 25˚C
104
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
105
If ∆G ≤ 0
spontaneous reaction
106
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
107
If ∆G ≥0
non-spontaneous reaction
108
If ∆G = 0
The system is in equilibrium
109
Redox reaction
A reaction in which both reduction and oxidation takes place
110
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
111
Reducing agent
A reagent that reduces (adds electrons to) another species
112
Oxidising agent
A reagent that oxidises (takes electrons from) another species
113
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
114
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 ...
115
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
116
Alternative cells use methanol as the fuel - advantages
liquid fuels are easier to store | methanol can be generated from biomass
117
Advantages of fuel cell vehicles
produce less pollution from exhaust gases (no NOx, CO, unburnt hydrocarbons) produce less CO2 more efficient
118
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
119
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)
121
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
121
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
122
What is entropy usually measured in?
joules
123
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
123
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

Chemistry Unit 5 (1 decks)

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