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AS level - Chemistry > Key definitions etc. > Flashcards

Key definitions etc. Flashcards

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1
Q

What is a radical

A

Atoms with an unpaired electron. They are formed from CFCs and by using UV Radiation and high energy radiation. Molecules can undergo homolytic fission and create radicals.

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2
Q

Explain why you cannot measure the enthalpy bond of formation of 2 reactants?

A

Because they don’t react together under standard conditions. There will be side products formed.

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3
Q

What is the CO bond in CO2?

A

A DOUBLE BOND (this is important for calculating bond enthalpy)

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4
Q

What is one main thing about concentrated acids?

A

They create a greater change in oxidation states.

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5
Q

How to obtain a more accurate value for the enthalpy change of combustion? (PAG related)

A

Insulate the can.

Burn the material in oxygen to ensure it is fully oxidised.

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6
Q

Explain Le Chatelier’s principle

A

There will be an equilibrium shift in an reaction to minimise the effects of a change in a condition

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7
Q

Define the enthalpy change of combustion

A

The enthalpy change for the complete combustion of 1mol of a substance under standard conditions (100kPa and 298K)

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8
Q

Define the enthalpy change formation

A

The enthalpy change when 1 mol of substance is formed from its elements under standard conditions.

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9
Q

If they ever ask you to calculate the enthalpy change of combustion, what is one thing to remember ?

A

ENTHALPY CHANGE OF COMBUSTION IS ALWAYS NEGATIVE

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10
Q

How can you identify for Fe?

A

Add NaOH and if it creates a green precipitate, Fe is present.

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11
Q

How can you identify non-polar and polar molecules?

A

If there is a lone pair of electrons on the central atom, then the molecule is polar.

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12
Q

Where is electronegativity the highest?

A

Generally, F is the highest in electronegativity. It increases from left to right, and from the bottom up.

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13
Q

What difference in electronegativity makes a bond polar?

A

0.4 - 1.7 means it is polar covalent

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14
Q

What is electronegativity?

A

An atom’s ability to attract a pair of electrons in a covalent bond.

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15
Q

Tests for halide ions

A

Add some drops of nitric acid.
Then some silver nitrate solution.
Observe the colour of the precipitate.

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16
Q

Testing for sulfate ions

A

Add barium chloride (or barium nitrate).

If a white precipitate is formed, then sulfate ions are present (as it create Barium sulfate)

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17
Q

Testing for carbonate ions

A

Add dilute HCl. Put any gas being formed to lime-water. If it turns cloudy, then the gas being formed is carbon dioxide.

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18
Q

How can you obtain an accurate value for the ethalpy change of combustion?

A

Insulate the can.
Put a lid of the can.
Burn the fuel in oxygen to ensure full oxidation.

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19
Q

How can you differentiate between alcohols?

A

Add acidified potassium dichromate (VI) annd tertiary alcohols will stay the same colour. But pirmary and secondary ones will change their colour (turn green)

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20
Q

Markownikoff’s Rule

A

When a HX reacts with an assymetrical alkene, the X will bond to the Carbon bonded to the most Carbons. Because a tertiary carbocation is more stable than a secondary one.

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21
Q

What are the 4 main stages in a simple generalised model of heterogeneous catalysis.

A

Stage 1 reactant(s) adsorbed/bond to surface of catalyst
Stage 2 (reactant) bonds (weaken) and break
Stage 3 (product) new bonds form
Stage 4 product(s) desorbed from surface of catalyst

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22
Q

What colour is iodine in cyclohexane

A

Purple

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23
Q

What colour is bromine in cyclohexane

A

Orange

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24
Q

What colour is chlorine in cyclohexane

A

Colourless

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25
Q

Are hydrogen bonding stronger than dipole-dipole interactions

A

Yes, they are. This means that they require more heat to break.

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26
Q

Difference between absorption and emission spectrum

A

The difference between absorption and emission spectra are that absorption lines are where light has been absorbed by the atom thus you see a dip in the spectrum whereas emission spectra have spikes in the spectra due to atoms releasing photons at those wavelengths.

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27
Q

How does the salt form in this reaction?

A

The hydrogen ion of the acid has been replaced by a metal ion

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28
Q

What is the one thing u should remember when you are writing equations for ionisation energies?

A

INCLUDE STATE SYMBOLS (always gases)

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29
Q

Why is a molecule polar?

A

Because the molecule is non-symmetrical and so the dipoles don’t cancel out. This means there is a net dipole on the molecule

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30
Q

What is the difference between a base and an alkali

A

A base is a substance that readily accepts H+ ions.

An alkali is a substance that releases OH- ions into aqueous solutions

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31
Q

What is a homologous series?

A

Same functional group
Same general formula
Each successive member differs by the addition of a CH2 group.
Same physical and chemical properties.

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32
Q

Name the 2 stages that’ll turn an alkane into an ethene.

A

fractional distillation and cracking.

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33
Q

What does “average bond enthalpy” mean

A

Average enthalpy change when one mole of bonds of gaseous covalent bonds is broken

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34
Q

Properties of a gas in an aerosol:

A 
Low reactivity 
Non-flammable 
Volatile 
Low boiling point 
Non-toxic.
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35
Q

What happens to a molecule when IR is absorbed?

A

The bond will vibrate and bend more.

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36
Q

Why may your value of Energy change be smaller than expected?

A

Incomplete combustion
Non-standard conditions
Evaporation of water or alcohol
Count towards the SHC of beaker.

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37
Q

Describe the relative energies of the 2s orbital and each of the three 2p orbitals in a
nitrogen atom.

A

p-orbitals have greater energy than s-orbitals

(three) p-orbitals have equal energy

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38
Q

Solid chlorine and solid bromine have a similar structure.

Name this structure.

A

Simple covalent

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39
Q

Main points in:
Explain the differences in the melting points of sodium and magnesium, using the model of
metallic bonding.

A

Just remember that the Mg has a greater attraction between the ions and the delocalised electrons.

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40
Q

Give the formula and the name of the compound formed between fluorine and sulfur
which has octahedral molecules.

A

SF6.

Called sulfurhexafluoride.

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41
Q

If you are going to produce X(OH)2 as a product, then the H20 you are reacting with, needs to be what state?

A

The H20 needs to be in a liquid state.

Otherwise, it will produce XO, when the H20 is in a gaseous state.

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42
Q

What shape is a F20?

A

Bent/ non-linear.

It has bond angles of 104.5

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43
Q

On a F20, what is the dipole?

A

Negative on the F, positive on the O.

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44
Q

In F20, what is the oxidation state of the O?

A

+2

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45
Q

Where are the ionisation numbers the highest?

A

It increases from right to left, and from bottom to top.

So the highest, is top right.

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46
Q

Define the second ionisation energies

A

It is the energy needed to remove a second electron from each ion in 1 mole of gaseous 1+ ions to give gaseous 2+ ions.

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47
Q

What is hydrolysis

A

When you break something down by adding water.

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48
Q

How carbon monoxide and nitrogen monoxide is made in catalytic converters, and emitted from cars.

A

Generally, they are formed due to incomplete combustion, so incomplete combustion equations for the reactions/ pollutants mentioned.
Then, talk about how a catalytic converter works.
Reactnats are absorbed onto surface, then the bonds are weakened. Then, the reaction takes place (the 2 pollutants react together, to form usually CO2 and N2). They desorb from the surface.

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49
Q

Structural isomers definition

A

Same molecular formula, but a different structural formula

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50
Q

Stereoisomers definition

A

Same molecular, and structural formula, but a different spacial arrangement

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51
Q

State two ways that the use of catalysts helps chemical companies to make their
processes more sustainable and less harmful to the environment.

A

Lower temperatures, lower pressures can be used.
Lower energy demand
Greater atom economy, so less waste, less use of toxic reactants

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52
Q

When drawing isomers from a peak on a mass spectrum

A

make sure to put charges (usually +)

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53
Q

State and explain the features of a hex-2-ene molecule that lead to E and Z isomers.

A

(carbon-carbon) double bond does not rotate
OR has restricted rotation
Each carbon atom of the double bond attached to (two)
different groups/atoms

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54
Q

With E=mc Change in T questions…

A

if they ever give you a density, then you should ALWAYS ALWAYS ALWAYS USE THE VOLUME TO CALCULATE THE MASS!!!

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55
Q

dm3 to m3

A

multiply by 10^ -3

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56
Q

Difference between pi-bonds and sigma bonds

A

Sigma bond is between bonding atoms/nuclei AND pi- bond is above and below the bonding atoms/nuclei.
sigma bond has direct/head-on overlap of orbitals AND pi- bond has sideways overlap. sigma bond has a lower bond enthalpy / is weaker than a pi-bond.
Sigma bond has electron density between bonding atoms AND Pi- bond has electron density above and below bonding atoms

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57
Q

When drawing OH bonds

A

never make it a horizontal OH bond!!

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58
Q

When naming isomers

A

make sure to put the Z/E in front of the isomer.

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59
Q

What is the formulae of vinegar?

A

CH3COOH

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60
Q

During a titration:
Suggest one assumption that the student has made that might mean that their calculated
concentration of ethanoic acid in the vinegar is invalid.
Predict, with a reason, how the experimental result would differ from the actual
concentration of CH3COOH if the assumption were not correct.

A

That the vinegar is pure, and contains no other acids. Otherwise the result would be greater.

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61
Q

Whenever calculating the Kc

A

always multiply the concentrations.

And it’s products/ reactants.

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62
Q

In any transition element questions

A

The 4S ELECTRONS ARE LOST FIRST!

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63
Q

How to calculate the EMF of a cell?

A

Reduction value - oxidation value.

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64
Q

Advantages of using fuel cells rather than fossil fuels

A

Only water is created- so there are no toxic products.

Has a greater efficiency

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65
Q

Disadvantages of using fuel cells rather than fossil fuels

A

H2 is difficult to store

H2 is difficult to manufacture initially.

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66
Q

Define the term “standard electrode potential”

A

The EMF of an electrochemical cell comprising a half cell combined with a standard hydrogen electrode at 1 atm, 298K, and all solutions at 1 moldm-3

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67
Q

Complete the diagram to show how the standard electrode potential of xyz can be measured.

A

Draw 2 half cells, connected by a salt bridge. In one, put a beaker thing with Hydrogen feeder inside it. That solution should be labelled as 1 moldm-3 H+ (aq). Put inside the hydrogen feeder, a platinum electrode.
In the other half cell, put in the normal electrode (AND LABEL THE IONS AND ELECTRODES!! WITH STATES!)

Connect the electrode together using a voltmeter.

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68
Q

Give one use for Chromium

A

Used for stainless steel because it can resist corrosion.

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69
Q

How to determine which half cell is reduction or oxidation?

A

Whichever is more positive is the reduction.

YOU HAVE TO SAY MORE POSITIVE!!! NOT HIGHER!!!

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70
Q

What are standard conditions for a electrochemical cell

A

Temperature of 298K, solutions at 1 moldm-3, and 100kPa pressure.

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71
Q

If they ask you about the oxidising ability of a specific chemical

A

Say that it’s EMF is more positive than the others, so it is a better oxidising agent.

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72
Q

When labelling an electrochemical diagram

A

PUT ALL IONS AND THEIR STATES!!!

it costs marks.

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73
Q

If they ask you what is oxidised and what is reduced

A

You have to say that xyz ION is oxidised, and xyz ION is reduced.

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74
Q

What colour is an acid on the pH scale?

A

Red

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75
Q

What colour is an alkali on the pH scale?

A

Violet/ blue

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76
Q

What colour is neutral on the pH scale?

A

Green

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77
Q

What is an aromatic compound?

A

They have a benzene ring in it.

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78
Q

What is an aliphatic compound?

A

No benzene ring.

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79
Q

When writing the equation of formation

A

The reactants are the elements itself, ALONE. You can’t have NaCl, but you can have Na + Cl2.

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80
Q

Hess’s law

A

The enthalpy change of any chemical change is independent of the route by which the chemical reaction occurs.

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81
Q

Equation for chlorine + NaOH to form bleach

A

2NaOH + Cl2 -> NaCl + NaClO + H20

Conditions: cold and dilute NaOH.

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82
Q

Equation for glucose + yeast:

A

C6H12 O6 -> 2C2H5OH + 2CO2

Has to occur in anaerobic conditions and betwen 20-45 degrees.

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83
Q

Catalytic converter reaction:

A

2NO + 2CO -> 2CO2 + N2

84
Q

Describe how London forces arise

A

The random movement of electrons causes an uneven distribution of negatvie charge, which creates an instantaneous dipole on a molecule. Then, this interacts with other neighbouring molecules to induce a dipole on them too.

85
Q

If you have a solution of NaI and another of NaCl. THen, you add in bromine water into each, and some cyclohexane, then what colour change will you see, what are the reactions that’ll tkae place and what does this tell you about the trend in reactivity?

A

Reactivity of the halogens decreases down the group. This is because the electron shielding increases down the group, and the nuclear attraction becomes smaller, making it harder to gain an electron and react. A halogen that is more reactive can take the place of a halogen that is less reactive.

When you add the Bromine water to the NaI, then the bromine will take place of the iodine. This is because bromine is more reactive than iodine. This means that you will gain Br- ions, and I2. There will be 2 layers in the test tube, where the organic laer will be a purple colour due to the I2.
(give ionic reaction)
When you add the bromine water to the NaCl, then no reaction will take palce. This is because chlorine is more reactive than bromine. There will be Br2 and Cl- ions, which means that in the test tube, there will be a colour change to orange due to the bromine.

86
Q

How could the student obtain a sample of magnesium phosphate after reacting magnesium with phosphoric acid?

A

Filter to obtain the solid and then evaporate the water (or dry the solid)

87
Q

Equation to find the EMF of a cell:

A

E = E(reduction) - E(oxidation)

88
Q

How to find the sign of an electrode:

A

It’s the same as the EMF value for each half cell.

89
Q

How does platin act in the treatment of cancer patients.

A

Platin binds to the DNA of cancer cells and stops them replicating.

90
Q

What is meant by one mole of substance?

A

(The amount of substance which contains) as many

particles as there are carbon atoms in 12g of 12C (atoms)

91
Q

Reasons for the order of anions test

A

Carbonates test is done first, because the barium ions will react with the carbonate ions to precipitate, giving a false positive.
Also, you add nitric acid before testing for halides because the solutions can easily absorb CO2 to form carbonate ions, which if reacting with Ba2NO3, then it will easily show a false positive for halides.

92
Q

If they ever ask for the molecular formula

A

Give it as “C4H802”, rather than “C3H7COOH”, because the second one is more structural formula.

93
Q

Whenever they ask you about boiling point of one being greater than the other

A

Refer to forces between them. As in x has hydrogen bonding, and y has permanent dipole-dipole interactions.
So x is harder to break, and requires more energy.

94
Q

What is stronger, hydrogen bonding or PD-PD?

A

Hydrogen bonding is a lot stronger.

95
Q

How do you know that all the impurity from a reaction has been removed/ the reaction has finished?

A

There will be no more fizzing, precipitation formed, or colour change etc.

96
Q

Whenever they talk about breaking things down

A

Say how they break (eg- by hydrolysis) and into their monomer units.

97
Q

If they ever ask you to draw optical isomers

A

Draw 3D diagrams

98
Q

Whenever talking about chiral centres?

A

Say that they are attached to 4 different groups, this allows it to produce mirror images of a compound, and create 2 enantiomers.

99
Q

When do you use cis/trans

A

For cis/trans, each Carbon on the double bond needs to be attached to another carbon or alkyl chain

100
Q

Disadvantages of producing a chiral drug as a mixture of stereoisomers. Then state some solutions to make only a single optical isomer

A

Disadvantages:

  • Cost/ difficulty in separating.
  • one stereoisomer might have harmful) side effects
  • reduces the (pharmacological) activity/effectiveness 

Synthesis of a single optical isomer

  • using enzymes or bacteria
  • using a chiral catalyst
    OR transition metal complex/transition metal catalyst
  • using chiral synthesis
    OR chiral starting material
    OR natural amino acid
101
Q

How can you manufacture ethanol

A 
Ethane 
Add phosphoric acid 
And steam 
300 degrees C
60-70 atm pressure
102
Q

Why does xyz not show optical isomerism

A

Because it doesn’t have a chiral carbon and so there is no asymmetry in the molecule

103
Q

What happens at the isoelectric point

A

A zwitterion is formed and the net charge is 0.

104
Q

Suggest an advantage of synthesising something starting form a natural steroid

A

It ensures that you create the correct isomer. So that way, you have to only make one and don’t need to spend money separating isomers.

105
Q

State ways polyester can be degraded

A

UV or photodegradable

Or hydrolysis

106
Q

Write the formula of H2N(CH2)4NH2 mixed with excess HCl

A

ClH3N(CH2)4NH3Cl

107
Q

Why would something be in zero order

A

Because it is in excess or it’s concentration doesn’t change.

108
Q

How does the ionisation energies change across a group

A

The number of electrons increases, increasing the atomic radius, and therefore the electron shielding.
The nuclear attraction on the outer electron decreases as well, and therefore the first ionisation energies decrease.

109
Q

How does the ionisation energies change across a period

A

Nuclear charge increases, shielding doesn’t increase, so that the nuclear attraction increases on the outermost electrons, leading to the atomic radius decreasing. This means that the first ionisation energy increases.

110
Q

Graphs of the first ionisation energies

A

It gradually increases across a period, but then goes all the way down for the next period, and starts increasing again.

111
Q

Weird cases for the first ionisation energies

A

2p4 is easier to remove than 2p3.
This is because there is electron repulsion between the 2 electrons, leading to a smaller energy required to separate them.
Why is it easier to remove a 2p electron than a 2s electron? Because the 2p is a higher energy electron,

112
Q

A proposed mechanism for this reaction takes place in several steps.
Suggest two reasons why it is unlikely that this reaction could take place in one step.

A

The rate equation doesn’t match the overall equation. Collision is unlikely with more than 2 ions.

113
Q

Whenever there is a compound, and they ask you why it is only x% effective/ thinking of isomers-

A

Write down how many chiral carbons there are and so how many enantiomers are made.
2 to the power of no. of chiral carbons.

114
Q

Why is a certain fatty acid more likely to be concerned with heart diseases?

A

Because it is a saturated.

115
Q

State 2 features that allow alkenes to show cis-trans isomerism

A

They have restricted rotation around the C=C double bond.

Each Carbon on the C=C double bond must be attached to 2 different groups or atoms.

116
Q

When something has a pH of 2.77 and it is put into a something with a high pH, how does the zwitterion change

A

You get COO- groups forming.
High pH means more alkaline- meaning you produce more OH-, so you have to remove the H+ ion from the COOH, and produce water, but you are left behind with COO-.

117
Q

What does a cyclic dieter look like?

A

It has 6 C atoms, and there are 2 ester bonds in the circle.

118
Q

Does C2O4 have a charge?

A

YES. -1

119
Q

What is Iodate(V) ions

A

IO3 -

120
Q

If I- is produced, and you want to check for the end point in a titration, what can you add

A

You should add starch.

It will turn a blue black solution to colourless.

121
Q

What causes the colour change from orange to green in the oxidation of alcohols?

A

Reduction of Cr 6+ to Cr 3+.

122
Q

Suggest why the reaction causes a mixture of products

A

Because substitution can occur on any of the positions on the ring, forming different isomers.

123
Q

How does amine act as a base

A

There is a lone pair of electrons on the Nitrogen atom, so it can accept a proton.

124
Q

How to write reduction equation

A

4[H]

125
Q

How can we use GC-MS to analyse a compound?

A

You can separate the compounds using the GC.

Then, you can compare the results using a database. You can also identify using the fragmentation ions.

126
Q

Define a nucleophile

A

The are electron pair donors

127
Q

Name common nucleophiles

A

OH-
H20-
NH3-

128
Q

Which C-X bonds are the strongest? The weakest?

A

The C- F bond is the strongest, and the C-I bond is the weakest. Therefore, the iodoalkanes react the fastest with nucleophiles, and the fluroalkanes react the slowest with nucleophiles.

129
Q

What can esters be used for?

A

Perfumes, flavouring.

130
Q

Difference between optical isomerism and stereoisomerism

A

Stereoisomerism is only used in alkenes.

Optical isomerism is when there are chiral carbon existing, and the carbon is connected to 4 different groups or atoms.

131
Q

If there are ever a LOT of peaks in a Carbon 13 NMR, but not too many in a Proton NMR

A

There is likely a benzene ring in there somewhere.

132
Q

How is NMR used in medicine?

A

NMR Imaging.

133
Q

How can you test for OH- ions?

A

Red litmus paper turns blue in the presence of OH- ions.

134
Q

Order of tests:

A

Carbonates -> hydroxides -> sulfates -> halides

135
Q

How many lone pairs of electrons are on the Oxygen in H2O?

A

There are 2 lone pairs.

136
Q

Alkene + water

A

Alcohol

137
Q

Which groups are 2,4 directing?

A

Don’t begin with C-

138
Q

Which groups are 3 directing?

A

Begin with C-

NO2 and C-N.

139
Q

Whenever dealing with amide /amine?

A

RTFQ!

DOES IT SAY AMIDE OR AMINE?

140
Q

Which compound is used as a standard for NMR chemical shift measurements?

A

Si(CH3)4

141
Q

What is an alicyclic compound

A

NO BENZENE RINGS

142
Q

Alkene + steam

A

Alcohol at the double bond.

143
Q

Amides bond breaking down - draw the structure of the salts

A

You can’t leave the charge alone. Salts should always have a net zero charge. So add NA+ etc. or as said in the question.

144
Q

How to go from g/dm3 -> mol/dm3

A

Divide by the Mr.

145
Q

Which of these organic compounds is more likely to be formed?

A

The element which is more electronegative will attach itself to the C bonded to the most Carbons. This is because the carbocation formed in this compound is more stable that the other one.
Then, show structures for both the compounds, saying one is more likely, and the other is less likely.

146
Q

NaOH + compound with OH and COOH

A

Turns into COO-Na+ and O-Na+.

147
Q

Na2CO3 + compound with OH and COOH

A

COO-Na+

148
Q

How to prepare a organic solid?

A

Recrystallise- dissolve in a minimum amount of hot solvent.
Then cool and filter under reduced pressure.
Scratch with a glass rod.
Wash with cold water or solvent
And then dry.

If needed to find purification- then find melting point and compare to known values using a database.

149
Q

CaCO3 + CH3COOH

A

2CH3COOH + CaCO3 → (CH3COO)2 Ca + CO2 + H2O

150
Q

What is the product when CH3COCl is attached onto benzene ring?

A

Phenylethanone

151
Q

What is a product with 2 COOH groups called

A

ex: Ethandioic acid

152
Q

Which is stronger polyamides or polyester

A

Polyester has a permanent dipole-dipole interactions.

Polyamides has Hydrogen bonding, which is stronger, so polyamides are stronger.

153
Q

Why is acyl chlorides better than COOH

A

A faster reaction

154
Q

Why are Anhydrides better than Acyl chlorides

A

They aren’t as violent of reactions.

155
Q

Is (CH3)NH more basic than ammonia?

A

Yes!!!
Because the alkyl group pushes the electron density towards the nitrogen atom- making it more attractive to electrophiles.

156
Q

What is the reaction where you turn a primary amine into a secondary amine by using a haloalkane?

A

A nucleophilic substitution

157
Q

Solubility of group 2 sulfates down the group

A

Decreases down the group

158
Q

Solubility of group 2 hydroxides down the group

A

Increases down the group

159
Q

Are alcohols polar?

A

Yes, they are polar. They have the -OH Bonding which makes it polar.

160
Q

How to show hydrogen bonding

A

Make a bond from the Oxygen of the alcohol to a hydrogen of the H2O molecule. AND- Always put 2 pairs of electrons on the Oxygen atom.

161
Q

Alcohol to alkene

A

Reflux with H3PO4.
Called a dehydration reaction or elimination.
Here, you may get isomers, as you can’t control where the double bond will go.

162
Q

What can be used as a drying agent?

A

Anhydrous MgSO4.

163
Q

What is a redox reaction/ what to look for when identifying a redox reaction?

A

Look at the oxidation states.

For a redox reaction, you should have an oxidation reaction and a reduction reaction.

164
Q

Which of the following is the correct procedure for rinsing glassware before beginning a titration?

  1. Rinse the burette with acid before filling with the acid solution.
  2. Rinse the pipette with distilled water before filling with alkali.
  3. Rinse the conical flask with alkali before adding a measured volume of the solution.
A

Only 1.

  1. is wrong because the pipette should be rinsed with the alkali that will be used, and not distilled water.
165
Q

Should you rinse the burette with acid before filling with the acid solution

A

Yes.

166
Q

How do group 2 metals react with water?

A

X(OH)2 + H2.

167
Q

How does the reactivity of group 2 metals change as you go down the group?

A

Increases- because they form 2+ ions.

168
Q

How does the alkalinity of group 2 hydroxides change as you go down the group?

A

The solubility of the hydroxides in water increases.
Therefore, the pH increases.
And so, the alkalinity increases.

169
Q

In terms of bond breaking, explain why this reaction is exothermic.

A

Bond breaking is exothermic, and bond making is endothermic.
Bond breaking absorbs energy and bond making releases energy.
In this reaction, more energy is released than absorbed.

170
Q

How to calculate the enthalpy change

A

Bond breaking - bond making.

171
Q

Enthalpy diagrams- which way is exothermic

A

Go down

172
Q

Why is the boiling point of AsH3 higher than PH3?

A

They both have a charge of -3.
As has more electron shielding, so it has a greater negative attraction, therefore it requires more energy to break than P.

173
Q

Note for explaining in equilibrium why something doesn’t have a high temperature despite it reaches a higher yield?

A

It is because high temperatures can use up a large amount of energy and fuel, not because it’s expensive.

174
Q

How to represent Partial pressure (used for gases only)

A

p(X)

175
Q

In a heterogeneous reaction, what states ARE included?

A

ONLY GASES AND AQUEOUS.

176
Q

Note for why does the group 2 elements Mg- Ba increase down the group

A

Don’t say that it is easier to remove the electrons, say that as you go down the groups, it requires less energy to react

177
Q

Proper definition of a disproportionate reaction

A

A reaction in which the same element is both oxidised and reduced.

178
Q

How to write an equation for the enthalpy change of atomisation of X

A

It MUST PRODUCE 1MOL OF THE PRODUCT!

ONLY 1 MOL OF PRODUCT

179
Q

What happens o Cu2+ in NH3

A

It forms Cu(OH)2.

Only in EXCESS nh3, it forms the complex ion with 4 NH3 and 2 H2P

180
Q

Uses of hydrogen

A 
Fuel cells
Hydrogenation of alkenes
Haber process
Making of HCl
Making of methanol
181
Q

How can an aqueous solution of an acid contain hydroxide ions?

A

Because the water also dissociates

182
Q

Reaction of CaCO3 and CH3COOH

A 
It produces (CH3COO)2Ca
If you will use ions, and signs, make sure to put the symbols on both the ions. OR just don't put them at all.
183
Q

Transition elements as catalysts

A

Haber process- iron catalyst.
Contact process- Vanadium(V) Oxide
Hydrogenation of margarine- Nickel.
Decomposition of hydrogen peroxide- MnO2.

184
Q

Features of Transition elements

A
  • Elements can act as catalysts
  • Different oxidation states
  • Have colourful compounds
185
Q

Weird cases for the electron configuration of transition elements

A

Copper and chromium:
They have 3d5 4s1 or 3d10 4s1.
It is better to have this than a nearly full or nearly half full 3d shell.

186
Q

Transition metals and oxygen

A

Each haem group has a Fe2+ ion.

The oxygen binds to this.

187
Q

Explaining why the temperature of a reaction is lower than it should be for an equilibrium reaction

A

Because a high temperature requires more energy and fuel.

188
Q

How to represent partial pressure of a substance

A

p(X)

189
Q

What states are included for the Kc expression of a heterogenous reaction?

A

Only gases and aqueous compounds

190
Q

Proper definition of a disproportionate reaction

A

A reaction in which the same ELEMENT is both oxidised and reduced.

191
Q

Explain why the reactivity of group 2 elements increases down the group

A

At the end, you have to say that there is less energy required for the reaction to occur.

192
Q

Why does As have a higher boiling point than P

A

Both have a charge of 3-.

As has more electron shielding. Therefore, it has a greater attraction, so more energy is required to break the bonds.

193
Q

How to write the reaction of Standard enthalpy change of atomisation

A

YOU MUST PRODUCE 1 MOL OF THE PRODUCTS.

ONE ONLY!!!

194
Q

Why should you always calibrate pH meters before using?

A

Because they can be affected by temperature changes.

195
Q

How to show the enthalpy change of reaction in a enthalpy profile diagram

A

Make sure to add the arrow to show which way the enthalpy change is.

196
Q

Chlorate (I)

A

ClO-

197
Q

Chlorate (VI)

A

ClO3 -1.

198
Q

How is the periodic table arranged?

A

Increasing proton number.
In periods, showing repeating trends in physical and chemical properties.
In groups, having similar chemical properties.

199
Q

What is metallic bonding

A

Strong electrostatic attraction between cations and delocalised electrons.
All metals have this giant metallic lattice structure.

200
Q

Use of Group 2 metals

A

Ca(OH)2 in agriculture to neutralise acidic soils.

Mg(OH)2 and CaCO3 as antacids in treating indigestion.

201
Q

Why can’t we use Ka to calculate the pH of stronger acids

A

Because the concentration of the acid at equilibrium may no longer be equal to the concentration of the acid at the beginning. (because it is for the weak acids)

202
Q

Example of a square planar complex ion

A

Pt(Nh3)2Cl2

203
Q

If you are told to react Mg (or any other metal with the charge of more than 1+) in an existing buffer solution, and are told to calculate the pH, what should you do?

A

Calculate the moles of the metal.
Multiply it by the magnitude of its charge (because then it creates a balanced reaction).
Then, add that moles onto the moles of the conjugate base (as you produce more), and take it away from the moles of the acid (as it will be used up instead).
Then, use the Ka to calculate the H+ concentration and eventually, the pH.

204
Q

What is the difference between the endpoint of a titration and the equivalence point?

A

The endpoint is when the colour changes, but the equivalence point is when the added titrant is chemically equivalent to the base.

205
Q

What does the stability of a compound based on?

A

A tertiary carbocation is more stable than a secondary carbocation. Also, the more alkyl groups attached to the Carbon atom, the more stable it is.

AS level - Chemistry (19 decks)

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