Chemistry - EEE Flashcards
(255 cards)
0
Q
What is the electron configuration of Chromium?
A
[Ar] 3d5, 4s1
1
Q
What is the electron configuration of Copper?
A
[Ar] 3d10, 4s1
2
Q
What is a transition element?
A
An element that forms one or more stable ions with a partially-filled d-subshell
3
Q
Why is scandium not a transition element?
A
Its only stable ion is Sc3+, which has a configuration of [Ar] 3d0
4
Q
Why is Zinc not a transition element?
A
Its only stable ion is Zn2+, which has a configuration of [Ar] 3d10
5
Q
what are the 4 typical characteristics of transition metals?
A
1) Variable oxidation state in compounds
2) The metals and their compounds are often catalytically
3) Able to form a wide range of complex ions
4) form coloured compounds
6
Q
Why do transition metals have variable oxidation states?
A
The energies of the 4s and 3d electrons are very similar
-> the elements can lose (or share) various number of electrons
when they form stable compounds
7
Q
Why are transition metals good catalysts?
A
They are good at absorbing reactants on the metal suface
thereby weaking the bonding in the molecule and hence lowering the activation energy
8
Q
Give examples of transition metals being used as catalysts
A
1) Catalytic Converters - Platinum, Rhodium, and Palladium
2) Haber Process - Iron metal
9
Q
Why are transition metal compounds often catalytically active?
A
They can easily and reversibly change oxidation states
- allows them to provide alternative reaction pathways in redox reactions
10
Q
Give an example of a transition metal compound being used as as catalyst
A
Vanadium Oxide - Catalyses oxidation of SO2 to SO3 in the manufacture of sulphuric acid
11
Q
What is a complex ion?
A
A metal ion bonded to a number of ligands by coordinate bonds (dative covalent bonds)
12
Q
what is a ligand?
A
An ion or molecule with a lone pair of electrons which it donates to a central metal ion by forming a coordinate bond with it
13
Q
In what 2 cases does the colour of a transition metal change?
A
1) When the oxidation state changes
2) When a complex ion with different ligands are formed
14
Q
What is the colour of iron in:
1) [Fe(H2O)6]2+
2) [Fe(H2O)6]3+
A
1) 2+: Pale green
2) 3+: Yellow
15
Q
What are the colours of the following ligands of cobalt:
1) [Co(H2O)6]2+
2) [CoCl4]2+
A
1) [Co(H2O)6]2+: Pink
2) [CoCl4]2+ : Blue
16
Q
What colour are the following compounds of Copper?
1) [Cu(H2O)6]2+
2) [Cu(NH3)4(H2O)2]2+
3) [CuCl4]2-
A
1) [Cu(H2O)6]2+ : Blue
2) [Cu(NH3)4(H2O)2]2+ : Deep blue
3) [CuCl4]2- : Yellow
17
Q
Write the equation of the reaction which is used as a test for the presence of Fe2+ ions, and the observation to confirm the reaction has occured
A
Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
Green Precipitate
18
Q
Write the equation of the reaction which is used as a test for the presence of Fe3+, and give the observation used as a positive result
A
Fe3+ (aq) + 3 OH- (aq) -> Fe(OH)3
Red/Brown Precipitate
19
Q
Write the equation of the reaction which is used as a test for the presence of Co2+, and give the observation used as a positive result
A
Co2+ (aq) + 2OH- -> Co(OH)2 (s) Blue Precipitate
20
Q
Write the equation of the reaction which is used as a test for the presence of Cu2+ , and give the observation used as a positive result
A
Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
Blue precipitate
21
Q
What are unidentate ligands?
A
Simple ligands which have a single point of attachment to the ion
22
Q
What are Bidentate Ligands?
A
a Lignad with 2 lone pairs, each capable of forming a coordinate bond to a metal ion
23
Q
what is the coordination number of an ion in a complex?
A
The number of ligand lone pairs that are bound to the ion - I.e. the number of co-ordinate bonds formed to the metal
24
What factor affects the co-ordination number of a compound?
Size of the ligands
25
What factor affects the shape of complex ions?
1) Size - **large ligands** and **small ions** favour **tetrahedral geometry - less crowded**
26
What is the bond angle in a tetrahedral complex ion?
109.5
27
what is the bond angle in a square planar complex ion?
90\* or 180\*
28
What are the bond angles in octahedral complex ions?
90\* or 180\*
29
Why may ligand substitution reaction occur?
1) One ligand can form **stronger coordinate bonds** to the metal ion than another
2) The substituting ligand is present in a **higher concentration** than the other
30
Give the equation and observation of the substitution reaction that occurs when Concentrated HCL is added to aqueous Cu2+
[Cu(H2O)6]2+ (aq) + 4Cl- [CuCl4]2- (aq) + 6H2O (l) Colour change from Blue to Yellow
31
Give the equation and observation of the substitution reaction that occurs when aqueous ammonia is added to aqueous Cu2+
1) when a **low conc. of ammonia** is added:
a) NH3 + H2O (l) -\> (NH4)+ + (OH)- (aq)
b) (Cu)2+ + 2(OH)- -\> Cu(OH)2 (s) observation: **Blue ppt**
2) High concentration NH3:
a) [Cu(H2O)6]2+ + 4NH3 -\> [Cu(NH3)4(H2O)2]2+ + 4H2O
observation: blue solution to **deep blue solution**
32
Give the equation and observation of the substitution reaction that occurs when concentrated HCl is added to aqueous Co2+
[Co(H2O)6]2+ + 4Cl- [CoCl4]2- + 6H2O
**Pink** solution turns **blue**
33
In Haemoglobin, what is the dentate of the Haem group ligand to the (Fe)2+ ion
Tetradentate (4)
34
What is the co-ordination number of Haemoglobin, and state the types of lone pairs in a haemoglobin molecule
1) 6 - octahedral
2) tetradentate haem group, protein, water
35
Give the ligand substitution of haemoglobin
let Hb = haemoglobin
Hb-H2O + O2 -\> Hb-O2 + H2O
36
Describe the process of the substitution reaction of haemoglobin in the body
- process allows Hb to transport O2 round the body
1) Forward reaction occurs in the lungs - High O2 concentration
2) In low O2 conc. (tissues) , backward reaction occurs - O2 released
37
Why does CO bind preferentially to oxygen in Hb?
- **CO** is a **better ligand than oxygen** - Binding affinity of CO 200X greater than O2
- \> low levels of CO dramatically reduce ability of Hb to carry O2
38
What are stereoisomers?
Same structural formula, different arrangement in space
39
Which types of ligand complexes does cis-trans isomerism occur in?
**Square planar** and **octahedral**
40
What orientation are a pair of ligands in if the bond angle between them is 90\*?
**Cis**
41
What orientation are a pair of ligands in if the bond angle between them is 180\*?
**Trans**
42
What is Cis - platin, and how does it work?
- Pt with 2 Cls and 2 NH3s [Pt(Cl)2(NH3)2]
- Used in treatment of cancer - stops tumour growth by **binding to DNA, stopping cell division**
43
Which ion complexes can exist as optical isomers, and under what circumstances?
- **Octahedral** - usually **2 or 3 bidentate ligands**
- **Tetrahedral** - only if **4 different ligands**
44
What does the bond angle in Ammonia change to when it acts as a ligand in a complex, and why does it change?
- **109.5** (from 107)
- NH3's **lone pair has been converted** to a **coordinate bond** - so **no lone pairs** in N's outer shell
45
What is the stability constant of a complex ion? give the symbol used also
**equilibrium constant** for the **formation of the complex ion** from its **constituent ions.** (water is discounted)
Kstab
46
What is an Acid?
A proton donor
47
What is a base?
A proton acceptor?
48
What name is given to the other part of an acid or base that remains unchanged in a reaction?
Spectator Ion
49
Why is the reaction of a metal element and an acid not an acid-base reaction?
H+ IS REDUCED
(no change of oxidation state in acid-base)
50
What is a strong acid? give an equation to demonstrate this
An acid which is **totally ionised in aqueous solution**
HCl (aq) -\> H+ (aq) + Cl- (aq)
51
What is a strong base?
A base which is **totally ionised in aqueous solution**
NaOH (aq) -\> Na+(aq) + OH- (aq)
52
What is a Weak Acid? give an equation to demonstrate this
an acid which is only **partially ionised in aqueous solution**
CH3COOH (aq) CH3COO- (aq) + H+ (aq)
53
What is a weak base? give an equation to demonstrate this:
A base which is **partially ionised in aqueous solution**
54
Write a Brønstead-Lowry equation for the ionisation of Hydrochloric acid:
HCl (aq) + H2O (l) -\> H3O+ + Cl-
55
What is the name of H3O+ (aq)?
HYDROXONIUM ION
56
What are Conjugate Pairs?
Acid-base pairs, differing only in the extra H+ possessed by the acid
57
What correlation is there between the strength of a conjugate acid and the strength of its conjugate base?
The **stronger the conjugate acid**, the **weaker the conjugate base**
(strong acid = equilibrium position of ionisation far to the right)
58
If two acids are involved in an acid-base reaction, how are their roles decided?
The stronger acid acts as the acid
59
What is the definition of pH?
pH= -Log[H+]
60
How do you find the concentration of H+, given pH?
10(-pH)
61
How do you calculate pH for a strong acid?
Strong acids are COMPLETELY IONISED, so
[Acid] = [H+] pH= -log[acid]
62
Give the equation for the equilibrium constant for the ionisation of water?
Kc = [H+][OH-]/[H2O]
63
What is Kw?
the IONIC PRODUCT OF WATER
Kw = [H+][OH-] Kw = Kc[H2O]
64
What is the value of Kw at 25ºc?
1x10-14 mol2dm-6 (on data sheet)
65
How the the ratio of H+ ions to OH- ions compare in a neutral solution?
SAME CONC OF H+ AND OH-
66
How the the ratio of H+ ions to OH- ions compare in an acidic solution?
HIGHER [H+] than [OH-]
67
How the the ratio of H+ ions to OH- ions compare in an alkali solution?
HIGHER [OH-] than [H+]
68
How would you calculate the pH of pure water at rtp?
Kw = [H+][OH-],
in pure water [H+] = [OH-]
Kw = [H+]^2
[H+] =√Kw
pH = -log[H+] = 7.00
69
What formula is used to calculate the pH of strong alkalis?
Kw = [OH-][H+]
[H+] =Kw/[OH-]
70
Why does the concentration of a weak acid not immediately indicate the concentration of H+?
Weak acids are NOT FULLY IONISED in aqueous solution
71
What constant is used to calculate [H+] of a weak acid?
the acid DISSOCIATION CONSTANT, Ka
72
How is Ka defined?
Ka = ([H+][A-])/[HA]
73
What are the units of Ka?
Moldm-3
74
What factor has an effect on the value of Ka?
TEMPERATURE
75
What does the value of Ka indicate about an acid?
LARGER Ka = STRONGER ACID (Higher H+ conc.)
76
What is pKa?
pKa = -logKa
77
why is pKa often used instead of Ka?
Ka is often a very small number
78
What effect does the strength of an acid have on pKa?
STRONGER ACID = SMALLER pKa
79
What is the general formula for calculating [H+] of a weak acid solution?
[H+] = √(Ka[HA])
80
What is assumed when calculating the pH of an acid, and in what case is this assumption not true?
[H+]=[A-]
-\> Only true for PURE ACIDS not true if extra acid or extra A- is added
81
What colour is MnO4-?
Purple
82
What is the colour of the end point of a potassium dichromate titration?
Pink
83
What is the colour change in iodine titrations?
Brown to colourless
84
What substance is often used to intensify the colour of iodine, and what colour does it turn in the presence of iodine?
Starch indicator Black
85
What are the characteristics of a dynamic equilibrium?
1) **Rate of forward reaction** = **rate of backward reaction**
2) **Closed system** - substances are not being added or removed
3) **macroscopic properties remain constant**
86
What is meant by Kc?
1) EQUILIBRIUM CONSTANT
87
Under what conditions is the value of Kc constant?
given TEMPERATURE
88
How does the value of Kc correlate with the position of equilibrium? for what conditions is this true?
**higher** Kc = position **further to right**
similar equilibria - Kc has **same unit**
89
What effect does an increase in temperature for an exothermic reaction have on the equilibrium constant, and why?
1) **decrease** in value of Kc
2) Position of equilibrium has shifted in the **endothermic direction - left**
90
What effect does an increase in temperature for an endothermic reaction have on the equilibrium constant, and why?
1) Kc **increases**
2) equilibrium shifts to **endothermic direction to oppose change - right**
91
What effect does an increase in pressure have on the value of Kc?
**No effect**
only effects position of equilibrium - will cause the equation to no longer equal Kc
92
How can we tell if a system has not reached equilibrium?
CONCENTRATIONS WILL NOT BE CONSISTENT WITH Kc
93
If the value of a concentration equation is higher than Kc, which way will the reaction move as it approaches equilibrium? why?
**Backward**
if calculated value is higher than Kc, **concentration on top line must be too high** compared to bottom line
concentration reaction will **move backward** (left) to **increase bottom line concentration**, and therefore come into line with Kc
94
What is the movement of electrons in a redox reaction?
electrons are transferred from the REDUCING AGENT to the OXIDISING AGENT
95
What name is given to the system where electrons flow indirectly from the reducing agent to the oxidising agent, causing an electric current?
ELECTROCHEMICAL CELL
96
Which electrode in a half cell contains the oxidising agent?
POSITIVE ELECTRODE
97
What is the purpose of a Salt Bridge?
to complete the circuit by allowing the controlled movement of IONS between the salt bridge (not electrons)
98
How can you construct a simple salt bridge?
A piece of filter paper soaked in saturated potassium nitrate solution
99
What is the correlation between cell potential and current?
Electrons move from a region of NEGATIVE POTENTIAL to an area of POSITIVE POTENTIAL
100
What is another term for voltage?
POTENTIAL DIFFERENCE
101
What is meant by cell potential?
The potential difference measured in a cell - measured in volts - always positive
102
What is the hydrogen electrode made out of?
Platinum - Hydrogen gas is bubbled over it in a H+ solution
103
What is the equation for the reaction at the hydrogen electrode?
H+ (aq) + e- \> 1/2 H2 (g)
104
What factor effects the direction the hydrogen electrode reaction goes in, and the charge of the hydrogen electrode?
How easily the other half cell is oxidised/reduced
105
What are standard conditions for a half cell?
1 moldm-3 solution 1 atm pressure 298K/25\*c temp
106
What is meant by Standard Electrode Potential?
The voltage measured in a cell which that half cell is connected to a standard hydrogen electrode, under standard conditions
107
How does the value of the standard electrode potential of a half cell affect whether it becomes the positive or negative electrode?
If E^ø is positive, when connected to a hydrogen electrode it will become the positive electrode
108
How does the reactivity of a metal correlate with the Standard Electrode Potential?
More reactive = reduction of ions **less favourable** = more negative E^ø
109
How would you make a half cell for a gas?
Bubble gas over Platinum electrode
and immerse in solution of ions
formed by reduction/oxidation of gas
110
How would you construct a half cell for ions of one element in solution?
Use a platinum electrode with BOTH IONS AT THE SAME CONCENTRATION
111
What is meant by Standard Cell Potential (E^ø cell)?
the DIFFERENCE between 2 E^ø values - always positive
112
How would you decide which half cell would be a negative electrode?
More negative E^ø = oxidation more likely = more negative electrode
113
How could you tell if a reaction is feasible from electrode potentials?
If the one with the more negative electrode potential is being reduced, it is not feasible
114
What factors may cause a measured E^ø value to be different form predicted E^ø values?
1) **non-standard conditions** - due to le chateliers principal - position of equilibrium shifts, affecting whether reduction or oxidation is more favourable
2) **rates of reaction** - **high activation energy**
- \> reaction occurs **too slowly** to come to equilibrium - changes measured E^ø
115
What is a storage cell?
An **electrochemical cell** with the voltmeter replaced by an **electrically powered device** (e.g. light bulb)
## Footnote
**The free energy created by the cell is used to create a voltage**
116
Why may an electrochemical cell with sufficient cell potential not be able to be used in practice,?
1) Salt bridge has HIGH RESISTANCE
117
What is an example of a storage cell?
NICKEL-CADMIUM BATTERIES
118
Why are nickel-cadmium batteries not widely used anymore?
1) HIGHLY TOXIC compounds - difficult to dispose of
2) EXPENSIVE - NON RENEWABLE
119
What type of storage cell are nickel-cadmium batteries?
RECHARGEABLE CELLS
120
What factor is necessary for a cell to be rechargable?
1) **electrodes must remain physically intact** as the reaction proceeds
- i.e cant change state -
**do not lose physicall integrity**
121
How would you recharge a cell?
1) connect **positive electrode to the positive terminal** of a power supply (and negative to negative)
2) **Electrons are driven back into the cell**
122
What is the difference between storage cells and fuel cells?
1) Storage cells are **sealed systems** - **the free energy is stored in the cell**
2) Fuel cells are not sealed - **chemicals constantly** **flow into the cell**
123
What 2 things do fuel cells generally require?
1) FUEL (usually HYDROGEN)
2) OXIDANT (usually OXYGEN from the air)
124
What are the electrodes in a Hydrogen fuel cell made out of?
Platinum catalyst coated metal
125
What is the reaction at the negative electrode in a hydrogen fuel cell?
1) 1/2 H2 -\> H+ + e-
Hydrogen is OXIDISED
126
What is the reaction at the positive electrode of a hydrogen fuel cell?
1) 2H+ + 1/2O2 + 2e- -\> H2O
127
What is the overall cell reaction for a hydrogen fuel cell?
H2 + 1/2 O2 -\> H2O
128
What is the reaction for the negative electrode of a hydrogen fuel cell under alkaline conditions?
1/2H2 + OH- -\> H2O + e-
129
What is the reaction for the positive electrode of a hydrogen fuel cell under alkaline conditions?
1/2 O2 + H2O + 2e- -\> 2OH-
130
What methods can be used for storing hydrogen in Fuel Cell Vehicles, and what are their limitations?
1) **High pressure** - risk of explosion, specialised tanks needed
2) **storage as liquid** - low temps required, expensive
3) **Adsorption on a solid surface** - expensive materials
4) **Absorption** **in a solid metal** - (release H2 as pressure eases)
5) **Hydrogen rich fuels** - H2 released by **reforming** - releases CO2
131
What are the advantages of FCV's?
1) (hydrogen FCVS) **only produce water as waste** - less polluting
2) **much more efficient** than traditional combustion engines - even reforming hydrogen rich fuels will produce less CO2
132
What are the limitations of FCV's?
1) **Hydrogen supply** - H2 doesn't occur on earth naturally, must be manufactured - costs energy and often produces CO2
2) **Hydrogen storage** - Compression and liquefaction have high energy costs and risks of explosion - Absorption and Adsorption systems for H2 have a limited lifetime
3) **Fuel cells** - need regular replacement - expensive to manufacture and involves toxic chemicals
133
What is meant by the Hydrogen Economy?
An economy in which our **energy needs are met to a substantial extent** by **hydrogen** in the place of fossil fuels
134
What obstacles need to be overcome in order to reach a hydrogen economy?
1) **Public and political acceptance** **of hydrogen as a fuel** - fear over explosion due to Hindenburg
2) **Establishment** **of infrastructure** **to ensure hydrogen** **is widely available** - storage and distribution facilities
3) **generation of large quantities** **of hydrogen**, **which requires energy** - will only significantly reduce CO2 emissions is fossil fuels are not used to generate H2 - electrolysis of water using sustainable energy sources
135
What is an Acid?
A substance that can donate a H+ ion
136
What is a base?
A substance that can accept a H+ ion
137
What name is given to ions in acid-base reactions that are not actively involved in the process?
SPECTATOR IONS
138
What is a strong acid?
An acid that is TOTALLY IONISED IN AQUEOUS SOLUTION HX -\> H+ + X-
139
What is a strong base?
A base that is TOTALLY IONISED IN AQUEOUS SOLUTION XOH -\> X+ + OH-
140
What is a weak acid?
An acid that is only PARTIALLY IONISED IN AQUEOUS SOLUTION HX H+ + X-
141
What is a weak base?
A base that only PARTIALLY IONISES IN AQUEOUS SOLUTION XNH2 + H2O XNH3+ + OH-
142
Write the Brønstead-Lowry equation for the ionisation of HCl:
HCl (aq) + H2O (aq) Cl- (aq) + H3O+ (aq)
143
What is the name of H3O+?
HYDROXONIUM ION
144
What is a Conjugate acid?
A Base which has accepted a H+
145
What is a conjugate base?
An acid which has donated a H+
146
What name is given to acid-base pairs that only differer by a H+ ion?
CONJUGATE PAIRS
147
How does the strength of a conjugate acid affect the strength of a conjugate base?
THE STRONGER THE CONJUGATE ACID, THE WEAKER THE CONJUGATE BASE
148
What is rate of reaction?
the rate of change of concentration of a reactant or product with time
149
What units are used to measure rate of reaction?
Moldm-3s-1
150
How can you measure rate of reaction on a graph plotting concentration against time?
Draw a tangent to curve at given time and measure gradient
151
What is meant by the Rate Equation of a reaction?
An equation showing how the rate depends on the concentrations of reactants
152
How do you write a rate equation?
Rate=K[A]m[B]n
153
How do you calculate the overall order of a reaction?
Sum all the separate orders in the rate equation
154
What name is given to the K in a rate equation?
Rate Constant
155
What is K a measure of?
The probability that a reaction will happen when the particles collide
156
What effect does temperature have on K, and why?
Increase in temp = increase in K Due to **increase in proportion** **of reactant molecules** **or ions** **with energy greater than the activation energy**
157
What effect do other variables - Concentration, pressure, etc. - have on the value of K?
NO EFFECT
158
What effect does the addition of a catalyst have on the value of K?
**May increase K** - but often **the entire rate** **equation changes** due to a new pathway with lower activation energy
159
What are the units of K?
Mol(1-x)dm(3x-3)S-1 Where x is the overall order of reaction
160
What is the half life of a reaction?
The time taken for the concentration of a reactant to fall to half of its original value
161
What is the trend in Half Lives for a zero order reaction?
SUCCESSIVE HALF LIVES DECREASE
162
What are the units of K for a zero order reaction?
Moldm-3s-1 (same as rate)
163
What does a rate v concentration graph look like for a zero order reaction?
Horizontal Line
164
What is the trend in half lives for 1st order reactions?
SUCCESSIVE HALF LIVES ARE CONSTANT
165
What are the units of K for first order reactions?
S-1
166
What does a Rate v concentration graph look like for first order reactions?
Positive gradient linear
167
What is the trend of half lives for second order reactions?
SUCCESSIVE HALF LIVES INCREASE
168
What are the units of K for second order reactions?
Mol-1dm-3s-1
169
What does a rate v concentration graph look like for a second order reaction?
Quadratic with positive gradient past origin
170
What are Enthalpy Profile Diagrams?
Diagrams which show the difference between the enthalpy of reactants and products
171
What are standard conditions for enthalpy change calculations?
100 kPa PRESSURE, SPECIFIC TEMP - 25ºc (unless stated otherwise)
172
What is the standard enthalpy change of a reaction?
The enthalpy change when the **number of moles** of **reactants** shown in an equation react together **under standard conditions**
173
What is the standard enthalpy change of formation? (/\Hf)
The enthalpy change when **one mole** of a compound is **formed** from its **elements** under **standard conditions**
174
For what group of compounds is /\Hf always negative?
ALL COMMON IONIC COMPOUNDS
175
What is bond enthalpy?
The enthalpy change required to BREAK ONE MOLE OF BONDS between TWO ATOMS in a GASEOUS STATE
176
What is the first ionisation energy of an element?
The energy needed to REMOVE ONE ELECTRON FROM EVERY ATOM IN EVERY ATOM IN ONE MOLE OF GASEOUS ATOMS in an element
177
What is the second ionisation energy of an element?
The energy required to remove ONE ELECTRON IN EVERY ION from ONE MOLE OF GASEOUS 1+ IONS OF AN ELEMENT
178
Why are all ionisations Endothermic? (+/\H)
Energy is needed to OVERCOME THE ATTRACTION BETWEEN OUTER ELECTRONS AND NUCLEUS
179
Why are second ionisation energies more Endothermic (more +ve) than first ionisation energies?
1) Same no of protons as 1st I.E., but 1 LESS ELECTRON
2) LESS REPULSION between remaining electrons
3) STRONGER ATTRACTION TO NUCLEUS
180
What is Hess' Law?
The enthalpy change in a chemical reaction is INDEPENDENT OF THE ROUTE taken by the reaction, provided the initial and final conditions are the same
181
What is the standard enthalpy change of atomisation?
The enthalpy change when ONE MOLE of gaseous atoms of an element are formed, FROM THE ELEMENT IN ITS STANDARD STATE
182
How does the trend in /\Hatomisation change as you go along a period, and why?
INCREASES ACROSS A PERIOD No. of outer shell electrons -\> MORE ELECTRONS CONTRIBUTING TO METALLIC BONDING
183
When is /\H atomisation not positive?
GROUP 8 ELEMENTS - exist as individual atoms
184
What is the first electron affinity of an element?
The enthalpy change when ONE ELECTRON is added to EACH ATOM in ONE MOLE OF GASEOUS ATOMS OF AN ELEMENT
185
What is the second electron affinity?
The enthalpy change when ONE ELECTRON is added to EACH ION IN A MOLE OF GASEOUS 1- IONS of an element
186
Why are all first electron affinities of elements that commonly form 1- ions negative?
The added electron is MORE STRONGLY ATTRACTED TO THE NUCLEUS than it is repelled by other electrons
187
Why are all second electron affinities positive?
ENERGY MUST BE PUT IN TO OVERCOME THE REPULSION between the negatively charged X- ion and e- that is added
188
What is lattice enthalpy?
the enthalpy change when ONE MOLE of the SOLID COMPOUND is FORMED form its GASEOUS IONS
189
What is lattice enthalpy a measure of?
The strength of ionic bonding in a compound
190
Are lattice enthalpies exo or endothermic?
Exothermic - when ions form ionic bonds, heat energy is released
191
What is the correlation between lattice enthalpy and strength of ionic bonds?
The more exothermic the lattice enthalpy, the STRONGER the ionic bonds
192
What is the main factor that affects lattice enthalpy?
CHARGE DENSITY
193
How does charge density affect the attraction of oppositely charged ions?
HIGHER CHARGE DENSITY = STRONGER ATTRACTION
194
How does the size of ions affect lattice enthalpy?
SMALLER IONIC RADIUS = GREATER CHARGE DENSITY -\> STRONGER ATTRACTION between ions = MORE EXOTHERMIC lattice enthalpy
195
How does charge affect lattice enthalpy?
GREATER CHARGE = GREATER CHARGE DENSITY -\> STRONGER ATTRACTION -\> MORE EXOTHERMIC
196
What is the correlation between lattice enthalpies and melting points?
HIGHER L.E. = HIGHER MPT as both depend on how much energy is needed to disrupt ionic lattice
197
What is the Enthalpy Change of Solution of an ionic compound?
The enthalpy change when 1 MOLE of a COMPOUND DISSOLVES IN WATER
198
What are the 2 steps that form the overall enthalpy change of solution?
1) BREAKING OF LATTICE - ENDOTHERMIC - overcoming attraction between oppositely charged ions - = LATTICE ENTHALPY WITH REVERSED CHARGE (+ve)
2) HYDRATION - EXOTHERMIC - ion-dipole forces form - addition of individual ions hydration enthalpies
199
What is meant by Enthalpy Change of Hydration?
Enthalpy change when ONE MOLE of gaseous IONS DISSOLVE to form ONE MOLE OF HYDRATED IONS
200
What factor affects the Enthalpy Change of Hydration of an Ion?
CHARGE DENSITY GREATER CHARGE DENSITY = STRONGER ION - DIPOLE FORCES = MORE EXOTHERMIC
201
What is entropy?
A measure of how disordered the particles in a system are
202
What happens to a system as entropy increases?
A SYSTEM BECOMES MORE ENERGETICALLY STABLE AS IT BECOMES MORE DISORDERED (higher entropy = more feasible reaction
203
What are the units for entropy?
JK-1Mol-1
204
What happens to the favourability of a system as the value of /\S increases?
Higher /\s = MORE FAVOURABLE
205
Why is a solid a low entropy state?
Particles are locked together in in a regular LATTICE -\> little freedom of movement = HIGHLY ORDERED = LOW ENTROPY
206
Why is a gas a high entropy state?
particles free to move = HIGHLY DISORDERED
207
When is the entropy change for the dissolution of a substance negative?
for some ions with very high charge density, as water molecules become more ordered
208
what is the formula for calculating /\s?
/\s = entropy of products - entropy of reactants (must times by no. of moles of substance in reaction)
209
What factors are favourable for a reaction to occur?
1) negative /\H
2) positive /\s
210
what is Free energy?
The balance between enthalpy and energy changes, which allow us to predict whether a reaction is feasible or not
211
What symbol is given to free energy change?
/\G
212
what is the formula for calculating /\G?
/\G = /\H - T/\s
213
how do you calculate T/\s?
# translate /\s units to kjK-1mol-1
(usually given in JK-1mol-1 - /1000)
convert temp from \*c to K (+273) =T
Tx/\s = T/\s
214
In order for a reaction to be energetically feasible, what value must /\G be?
/\G\<0
215
Why may a reaction still not happen, given that /\G is negative?
high activation energy
216
What conditions are necessary for an endothermic reaction to be feasible?
ENTROPY INCREASES IN FORWARD REACTION - +/\S
217
What is the definition of pH?
-log10[H+]
218
How would you find the pH of a strong acid?
[acid] = [H+] pH = log10[H+]
219
What is Kw?
The IONIC PRODUCT OF WATER,
Kw = [H+][OH-] ( constant at given temp - value on data sheet)
220
What is the ratio of H+ to OH- in a neutral aqueous solution?
Equal concentrations
221
What is the ratio of H+ to OH- in an acid aqueous solution?
Higher conc of H+ than OH-
222
What is the ratio of H+ to OH- in an alkali aqueous solution?
Higher conc. OH- than H+
223
How would you calculate the pH of a strong alkali solution?
[H+] =Kw/[OH-]
224
What do you need to be able to work out the pH of a weak acidic solution?
DISSOCIATION CONSTANT (Ka)
225
What is Ka defined as?
Ka = [H+][A-]/ [HA]
226
What are the units of Ka?
Moldm-3
227
What is the relationship between the value of Ka and the strength of an acid?
LARGER Ka = higher [H+] = STRONGER ACID
228
What is pKa?
-Log10[Ka]
229
What is the correlation between the strength of an acid and the value of pKa?
STRONGER ACID = bigger Ka = SMALLER pKa
230
What assumption must be made to calculate the pH of a weak acid?
[H+] = [A-], will not apply if extra acid or salt is added
231
What is the formula for calculating the [H+] of a weak acid?
[H+] = √(Ka[HA])
232
What is meant by the Equivalence Point of a titration curve?
The point at which just enough acid has been added to neutralise the alkali solution the steep, almost vertical point of a pH curve
233
What shape will the acidic portion of a curve have if the acid is strong?
exponential curve up to equivalence, vertical part reaches to a quite low pH
234
What shape will the acidic portion of a curve have if the acid is weak?
Gradual, almost linear gradient of increase in pH up to equivalence point, reaches vertical point around pH 7
235
What shape will the alkali portion of a pH curve have if the alkali is strong?
logarithmic shape to the curve, vertical point finishes around pH 10
236
What shape will the alkali portion of a pH curve have if the alkali is weak?
linear curve, starts around pH 8 will level out at a lower pH, but will not fully reach the pH of the pure alkali added
237
How would you choose a suitable indicator for a titration curve?
The pH RANGE OF THE INDICATOR SHOULD BE WITHIN THE VERTICAL SECTION OF THE CURVE
238
What would be observed if an unsuitable indicator was chosen, and why?
GRADUAL COLOUR CHANGE will not reach/already past EQUIVALENCE POINT - CURVE IS NOT VERTICAL IN INDICATORS pH RANGE
239
What is the standard enthalpy change of neutralisation?
THE CHANGE IN ENTHALPY WHEN AN ACID AND BASE UNDERGO A NEUTRALISATION REACTION TO FORM \*ONE MOLE OF WATER\* UNDER STANDARD CONDITIONS \*any ∆H neutralisation reaction equations must be scaled to form one mole of water
240
What equation is used to calculate enthalpy change of neutralisation?
mc∆T (Results in J - may need to convert to kJmol-1
241
Why cant mc∆T be used to calculate the enthalpy change of neutralisation of weak acids and bases?
The ionisation of the acid/base will also contribute something to the overall enthalpy change
242
What is a buffer solution?
A system that MINIMISES pH changes on addition of an acid or base
243
What is an acidic buffer solution formed out of?
A WEAK acid and its CONJUGATE BASE
244
What happens if acid is added to an acidic buffer solution?
BEFORE EXTRA ACID IS ADDED: XH X- + H+ WHEN ACID IS ADDED: If a small amount of another acid is added to the buffer solution, most of the H+ ions are removed by the reaction with the CONJUGATE BASE X- ( i.e. by the BACK REACTION OF THE DISSOCIATION EQUILIBRIUM) X- + H+ -\> HX So [H+] doesnt change much = pH is only slightly changed
245
Describe the action of a buffer solution in terms of Le Chatelier's Principle?
When acid is added to the Buffer, the increase in H+ is opposed by the equilibrium shifting to the left, and forming HX
246
Give the overall equation for the reaction that takes place when more alkali is added to an alkali buffer solution:
YOH + OH- YO- + H2O
247
How would you calculate the pH of a buffer based on a weak acid, HA and its salt, A-?
[H+] = Ka x ([HA]/[A])
248
Under what conditions is a buffer solution most effective?
1) if it contains substantial amounts of acid and conjugate base 2) when pH is close to pKa (if pH = pKa, concs are equal) 3) One pH unit either side of pKa
249
Give an equation for a basic buffer:
NH3 + H2O NH4+ + OH-
250
What is the equation for the equilibrium of the dissociation of CO2 in water (e.g. in blood)?
H2O + CO2 H2CO3 (carbonic acid)
251
What is the equation for the reaction that forms a buffer solution in blood?
H2CO3 H+ HCO3-
252
How is blood CO2 concentration maintained, and how is H2CO3 produced?
1) CO2 is produced in respiration and dissolves in blood, forming H2CO3, and is breathed out in the lungs at the same rate
253
How is a roughly constant HCO3- concentration maintained in the body?
excess ions are reabsorbed in the kidney
254
Why is maintenance of the bloods pH important?
Enzymes that control the bodys biochemistry only work over a narrow pH range
