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Chemistry A Level Key Knowledge > Chemistry Key Definitions And Things To Remember > Flashcards

Chemistry Key Definitions And Things To Remember Flashcards

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1
Q

Define The Standard Enthalpy Of Formation.

A

The enthalpy change when one mole of a compound is formed from its elements under standard conditions, all reactants and products in their standard states.

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2
Q

Define The Standard Enthalpy Of Combustion.

A

The enthalpy change when one mole of a compound is completely burned in oxygen under standard conditions, all reactants and products in their standard states.

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3
Q

Define The Standard Enthalpy Of Atomisation.

A

The standard enthalpy change when one mole of gaseous atoms is formed from an element in its standard state.

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4
Q

Define Mean Bond Enthalpy (Aka bond dissociation enthalpy).

A

The enthalpy change when one mole of gaseous molecules each break a covalent bond to form to free radicals (atoms), averaged over a range of compounds.

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5
Q

Define 1st Ionisation Enthalpy.

A

The standard enthalpy change when one mole of electrons is removed from one mole of gaseous atoms to give one mole of gaseous ions with a single positive charge.

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6
Q

Define 2nd Ionisation Enthalpy.

A

The standard enthalpy change when one mole of electrons is removed from one mole of gaseous 1+ ions to give one mole of gaseous ions each with a 2+ charge.

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7
Q

Define 1st Electron Affinity.

A

The standard enthalpy change when one mole of gaseous atoms is converted into a mole of gaseous ions each with a single negative charge under standard conditions.

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8
Q

Define 2nd Electron Affinity.

A

The standard enthalpy change when one mole of electrons is added to a mole of gaseous ions each with a single negative charge, to form a mole of ions each with a two negative charge.

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9
Q

Define Lattice Formation Enthalpy.

A

The standard enthalpy change when one mole of a solid ionic compound is formed from its gaseous ions.

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10
Q

Define Lattice Dissociation Enthalpy.

A

The standard enthalpy change when one mole of a solid ionic compound dissociates into its gaseous ions.

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11
Q

Define Standard Enthalpy Of Solution.

A

The standard enthalpy change when one mole of a solute dissolves in enough solvent to form a solution in which the ions are far enough apart to not interact with each other.

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12
Q

Define The Standard Enthalpy Of Hydration.

A

The standard enthalpy change when one mole of gaseous ions is converted to one mole of aqueous ions.

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13
Q

Define Hess’s Law.

A

The enthalpy change for a chemical reaction is the same, regardless of the route taken from reactants to products.

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14
Q

State the meaning of the term periodicity.

A

Repeating patterns/trends of physical or chemical properties across a period.

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15
Q

If something can act as either an acid or base, it is:

A

Amphoteric

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16
Q

Give the percentage uncertainty equation.

A

% Uncertainty = (uncertainty/value measured) x100

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17
Q

What is the half neutralisation point of a pH curve?

A

The point when enough base has been added to neutralise exactly half of the acid (or vice versa). On a pH curve: half way between 0 and equivalence point on x-axis. [HA]=[A-] so equal moles of salt and acid so Ka=[H+] therefore pKa=pH.

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18
Q

What are the bond angles and shape for a molecule with 2 bonding pairs?

A

Linear, 180°

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19
Q

What are the bond angles and shape of a molecule with 3 bonding pairs?

A

Trigonal Planar, 120°

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20
Q

What are the bond angles and shape of a molecule with 4 bonding pairs?

A

Tetrahedral, 109.5°

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21
Q

What are the bond angles and shape of a molecule with 5 bonding pairs?

A

Trigonal Bipyramidal, 120° and 90°

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22
Q

What are the bond angles and shape of a molecule with 6 bonding pairs?

A

Octahedral, 90°

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23
Q

What are the bond angles and shape of a molecule with 2 bonding pairs and 1 lone pair?

A

V-Shaped, 117.5° (120-2.5 as one lone pair)

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24
Q

What are the bond angles and shape of a molecule with 3 bonding pairs and 1 lone pair?

A

Trigonal Pyramidal, 107° (109.5-2.5 as one lone pair)

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25
Q

What are the bond angles and shape of a molecule with 2 bonding pairs and 2 lone pairs?

A

V-Shaped, 104.5° (109.5-2(2.5) as 2.5 for each lone pair)

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26
Q

What are the bond angles and shape of a molecule with 4 bonding pairs and 1 lone pair.

A

Seesaw Molecule, 119°, 89° (More than 5 e- pairs so different rules, angles from original structure have 1° subtracted from them)

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27
Q

What are the bond angles and shape of a molecule with 3 bonding pairs and 2 lone pairs? (Two answers)

A

T-Shaped, 89° (90-1, despite having two lone pairs. You just need to know this one, don’t try and figure it out with logic)
Or
Trigonal Planar, 120°, lone pairs are in an axial position (on opposite sides) so their stronger repulsion cancels each other out leaving, a trigonal planar shape as if they didn’t exist in the first place (still draw them though)

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28
Q

What are the bond angles and shape of a molecule with 5 bonding pairs and 1 lone pair?

A

Square Pyramidal, 89° (more than 5 pairs so different rules. 90-1 as original structure is octahedral but one lone pair instead of a bonding pair)

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29
Q

What are the bond angles and shape of a molecule with 4 bonding pairs and 2 lone pairs?

A

Square Planar, 90°, Lone e- pairs in axial position (Opposite each other) so their stronger repulsions cancel out leaving essentially an octahedral, 90°, but without the top and bottom bonding pairs.

30
Q

Give an equation to represent the ionisation of a molecule ‘X’ in Electrospray Ionisation.

A

X(g) + H+ —> XH+(g)
(Remember, when looking at the mass spectrum, the Mr will be the Mr of ‘X’ +1 as it had gained a proton, so its actual relative molecular mass one subtracted from the value in the spectrum)

31
Q

Give an equation to represent the ionisation of a molecule ‘X’ in Electron Impact Ionisation.

A

X(g) —> X+(g) + e-

Electrons collide with electrons in molecule, ionising them

32
Q

Heterogeneous Catalyst Example, Haber Process. Name catalyst and show reversible equation (making ammonia)

A

Catalysed by Solid Fe

3H2+N2 (reversible arrow) 2NH3

33
Q

Heterogeneous Catalyst Example
Contact Process
Name catalyst and show reaction equation (making sulfuric acid) and catalyst reformation.
Give a suggestion for the use of the product

A

Vanadium (V) Oxide
SO2(g) + V2O5(s) —> SO3(g) + V2O4(s)

V2O4(s) + 1/2O2(g) —> V2O5(s)
Used to make sulfuric acid (group 3)
SO3 + H2O —> H2SO4

34
Q

Heterogeneous Catalyst Example

Manufacturing of methanol

A

Solid Cr2O3 Catalyst
CH4(g) + H2O(g) –> CO(g) + 3H2(g)
CO(g) + 2H2(g) –> CH3OH(g)

35
Q

How does a solid Heterogeneous Catalyst work for gas/liquid reactants

A
  • Reaction occurs on the active sight of the surface of the catalyst
  • Reactants adsorb into surface
  • Bonds weaken
  • Reaction occurs
  • Products desorb from the surface
36
Q

How to make a solid Heterogeneous Catalyst more efficient

A

Increase its surface area and spread it over an inert support medium

37
Q

How do solid Heterogeneous Catalysts get poisoned? And how is it prevented?

A

-Impurities block the active sights
(Stronger adsorb and don’t desorb)
-Purifying the reactants prevents poisoning

38
Q

For Homogeneous Catalyst Reaction,
Peroxudisulfate ions to oxidise iodide ions to iodine, give the half equations uncatalysed and explain why this his high activation energy

A 
S2O8^2- + 2e- --> 2SO4^2-
2I- ---> I2 + 2e-
So overall
S2O8^2- + 2I- ---> 2SO4^2- + I2
Which has two -ve ions reacting and therefore they repel, so high Ea
39
Q

For Homogeneous Catalyst Reaction,
Peroxudisulfate ions to oxidise iodide ions to iodine, give the half equations catalysed and name the catalyst. Explain why this has a much lower Ea

A 
Catalysed by Fe2+ ions in 2 step process
(Or Fe3+ and swap steps 1 and 2)
Step 1:
2Fe2+ ---> 2Fe3+ + 2e-
S2O8^2- + 2e- ---> 2SO4^2-
Step 2 (Catalyst Re-Formed)
2I- ---> I2 + 2e-
2e- + 2Fe3+ ---> 2Fe2+
Has +ve and -ve ions reacting so they attract so low Ea
40
Q

Give the half equations for the reaction you need to know for Autocatalysis when uncatalysed and explain the low Ea
(Oxidation of ethanedioc acid by manganate (VII) ions)

A

5e- + 8H+ MnO4- —> Mn2+ + 4H2O
C2O4^2- —> 2CO2 + 2e-
High Ea as two -ve ions repel

41
Q

Give the half equations for the reaction you need to know for Autocatalysis when catalysed by its own product, and mention what the product is and why it decreases Ea

A 
Catalyst: Mn2+
Step 1:
5e- + 8H+ + MnO4- ---> Mn2+ + H2O
Mn2+ ---> Mn3+ + e-
Step 2: 
C2O4^2- ---> 2CO2 + 2e-
2e- + 2Mn3+ ---> 2Mn2+

-ve ions and +ve ions attract so low Ea

42
Q

Explain concentration against time graph for Autocatalysis reaction

A
  • Slow rate at start
  • As no catalyst initially
  • So high Ea as two -ve ions react
  • More Mn2+ formed so faster rate
  • Due to increasingly catalyst reaction
  • Rate decreases again and levels off
  • As reactants get used up
43
Q

Give the colour change for MnO4- —> Mn2+

A

Purple to colourless

44
Q

To form Vanadium (II), (III) and (IV) ions from Vanadium (V), what is required, and what is the colour of Vanadium (V)

A

Zinc (Zn) to be oxidised to Zn2+

Colour: Yellow

45
Q

Colour of Vanadium ions, from (V) to (II)

A 
Ya.                  Yellow.  (V) 
Bastard.        Blue.    (IV)
Got                 Green.  (III)
Punched.       Purple. (II)
Going down (like the bastard) form V
46
Q

What happens to Cobalt (II) hexa-aqua ions in Alkaline conditions?
E.g H2O2, NH3, or O2

A

Oxidised to Cobalt (III)

47
Q

Half equations for Cobalt (II) Hexa-aqua ions (acts as acid) reacting with H2O2 (base so dissociation)

A

H2O2 + 2e- —> 2OH-

[Co(OH)6]4- —> [Co(OH)6]3- + e-

48
Q

Equations for the reaction of Cobalt (II) hexa- aqua ions with NaOH (like the same reaction with Cu instead) and give the colour change

A

[Co(H2O)6]2+(aq) + 2OH- —> Co(H2O)4(OH)2 + 2H2O

Pink solution to blue ppt

49
Q

Reaction of Co(H2O)4(OH)2 with NH3 and state colour change

A

Reaction of Co(H2O)4(OH)2 + 6NH3 —> [Co(NH3)6]2+ (aq) + 4H2O + 2OH-
Blue precipitate to pale brown solution

50
Q

Give the half equations for the reaction of [Co(NH3)6]2+ (aq) with O2 and H2O

A

O2 + 2H2O + 4e- —> 4OH-

[Co(NH3)6]2+ (aq) —> [Co(NH3)6]3+ (aq) + e-

51
Q

Give the colour change for Fe2+ to Fe3+

A

Green to brown

52
Q

Give the colour change for Cr2O7 2- to Cr3+

A

Orange to green

53
Q

How are Transition Metal Ions Coloured?

A
  • Transition metals are coloured due to partially filled d-sub shell
  • In pure transition metal, d-orbitals are of equal energy AKA ‘ground state’
  • In transition metal compounds, due to other atoms present, d-orbitals have slightly different energies
  • So e- can be excited from one d-orbital to another
  • When one e- moves from lower energy d-orbital to a higher one, energy is needed to make the transition.
  • This energy is taken from white light and a specific wavelength of light is absorbed which is missing from the light that gets reflected/transmitted to give the compound it’s colour.
54
Q

What are the steps of using Colorimetry for finding the concentration of a solution

A
  1. Multiple samples if known different concs of solution, with appropriate ligand added to intensify the colour
  2. Test each known sample for transmittance/absorbance
  3. Plot Conc Vs transmittance graphs
  4. Test solution of unknown concentration for transmittance
  5. Use graph to find corresponding concentration

(Transmittance -> 1.0 = All light passed through, 0.5=50% absorbed, 0=All light absorbed)

55
Q

What happens when chlorine is added to water, what type of reaction is it and why is the product useful?

A

Cl2 + H2O HClO + HCl
Disproportionation (Oxidised and Reduced)
HClO kills bacteria

56
Q

How is bleach made? (NaClO)

A

Cl2 + 2NaOH —> NaClO + NaCl + H2O

57
Q

What happens when Chlorine reacts with water in sunlight?

A

2Cl2 + 2H2O —> 4HCl + O2

58
Q

What does CRAM stand for and how do we use it to distinguish which has the more exothermic lattice formation enthalpy, MgO or Na2O

A

Charge, Radius, Attraction, More exothermic or endothermic
Mg2+ has greater charge than Na+, and a smaller atomic radius so a greater attraction to O2- so MgO has a more exothermic lattice formation enthalpy

59
Q

When conditions change for an electrode, what may happen? (e.g altered temp, Conc, pressure)

A

Equilibrium position will shift
More or less e- produced
Larger or smaller E°
Affects calc

60
Q

What is a salt bridge and what is its purpose?

A

Salt bridge is a solution and connects both beakers. It’s ions are free to move and balance the charges in either electrode.
It must be UNREACTIVE with half cells. (KNO3 usually used)

61
Q

If two metal ions have SAME state, how are they indicated in cell representation?

A

With a comma

62
Q

When given a table of electrode potentials what is the main rule?

A

For most positive E°, SOWR
strongest oxidising agent on left
Weakest reducing agent on right

63
Q

When are platinum electrodes used?

A

When no solid metal in reaction, so metal ions with two diff charges in same solution
E.g FeSO4 and Fe2(SO4)3 is a solution of Fe2+ and Fe3+
It is unreactive but still conductive

64
Q

What is the half equation for a standard hydrogen electrode? And what are the conditions? Does the other electrode need the conditions?

A

2H+ + 2e- (reversible arrow) H2
Temp: 298k Conc: 1moldm-3 of H+ sol (e.g 1moldm-3 of HCl or 0.5moldm-3 of H2SO4)
Pressure: 100KPa
Connected electrode must also have these same conditions

65
Q

How can you test for Ammonium Ions

A

Add NaOH
NH4+ + -OH —> NH3(g) + H2O
Red litmus paper turns blue

66
Q

What is an example of a reachable battery?

A

Lithium Ion battery

67
Q

What occurs at the negative electrode of a lithium Ion battery?

A

Graphite (carbon) with a layer of Li(s) on it dissociates

Li(s) –> Li+ + e-

68
Q

What happens on the positive electrode of a lithium ion battery

A

Li+ ions and CoO2 from electrolyte (both have same state) form lithium cobalt oxide Li(CoO2)(s) on a platinum electrode
CoO2 + Li+ + e- —> Li(CoO2)

69
Q

For an alkaline membrane hydrogen oxygen fuel cell, give the half equation for the anode (negative electrode) and the cathode (positive electrode).

A

H2(g) + 2OH-(aq) reversible arrow 2H2O(l) + 2e-

0.5O2(g) + H2(g) + 2e- reversible arrow 2OH- (aq)

70
Q

For an acidic membrane hydrogen oxygen fuel cell, give the half equation for the anode (negative electrode) and the cathode (positive electrode).

A

H2(g) Reversible Arrow 2H+(aq) + 2e-

0.5O2(g) + H2(g) + 2e- reversible arrow H2O(l)

Chemistry A Level Key Knowledge (2 decks)

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