Module 3

Question 1

What is ionisation energy?

Answer 1

Measures how easily an atom loses electrons to form positive ions.

Question 2

What is the first ionisation energy?

Answer 2

Energy required to remove one electron from each atom in one mole of gaseous atom of an element to form one mole of gaseous 1+ ions.

Question 3

Factors affecting ionisation energy

Answer 3

Atomic radius
Nuclear charge
Electron shielding

Question 4

Why does beryllium have a higher ionisation energy than boron

Answer 4

Boron marks the start of filling in the 2P sub shell and therefore it is easier remove the one electron than to remove one of the electrons of the 2s sub shell in beryllium.

Question 5

Why does nitrogen have a higher ionisation energy than oxygen?

Answer 5

One of oxygens 2P orbitals is paired unlike nitrogen and therefore the two electrons repel each other making it easier to remove an electron from oxygen than nitrogen.

Question 6

What is a giant covalent bond?

Answer 6

Where many billions of atoms are held together by only covalent bonds to form a giant covalent bond.
They’re usually- boron, carbon, silicon.

Question 7

Group 2 reactivity trends

Answer 7

Becomes more reactive as you go down, this is because:
More electrons
Increase in atomic radius
Lower ionisation energies
Shielding increases

Question 8

How do halogens exist in RTP?

Answer 8

As diatomic molecules

Question 9

What is the trend of boiling point in Halogens

Answer 9

Boiling point increases.
As:
More electrons
Stronger london forces
More energy required to break the intermolecular forces.

Question 10

Halogen-Halide displacement reactions (testing)

Answer 10

In water: pale green = Cl, orange = Br, Brown = I

Cyclohexane: pale green = Cl, orange = Br, Violet = I

Question 11

Explain the displacement reactions of halogens.

Answer 11

Cl can displace both Br ions and Iodine ions.
Br only displaces iodine ions.
Therefore halogens are less reactive as you go down.

Question 12

Explain the trend in reactivity of Halogens.

Answer 12

As you go down the group reactivity decreases. As halogens need to gain an electron which is hard as you go down.
This is because:
- atomic radius increases
- more inner shells so shielding increases
- so less nuclear attraction to capture an electron from another species

Question 13

What is disproportionation reactions?

Answer 13

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

Question 14

Give an example of a disproportionation reaction?

Answer 14

Chlorine with water:
Cl2 (aq) + H2O — HClO (aq) + HCl (aq)
These products can be used to kill bacteria rather than just using harmful pure chlorine.

Question 15

Reaction of chlorine with dilute, cold aqueous sodium hydroxide.

Answer 15

Cl2 (aq) + 2NaOH (aq) — NaCl + H2O + NaClO
Also a disproportionation reaction.

Question 16

What are the benefits of Chlorine?

Answer 16

Ensures water is fit to drink.
Used for bleach.
Can kill bacteria.

Question 17

What are the risks of Chlorine?

Answer 17

Extremely toxic gas
Respiratory irritant and can be fatal in a large quantity.
Chlorine in drinking water could react with organic hydrocarbons like methane.
But the risks of not adding the minimum amount of chlorine to water is far more lethal than risks posed by the hydrocarbons.

Question 18

What is the test for halide ions?

Answer 18

Precipitation reactions with aqueous silver ions.
AgCl = White, AgBr = Cream, AgI = Yellow.

Question 19

Qualitative analysis for ions.

Answer 19

1. Carbonate test- Add dilute nitric acid, if you see bubbles, there is carbonates present. To further prove the gas is CO2 you can bubble it through lime water.
2. Sulphate test- Add barium ions, if a white precipitate forms, it must contain a sulphate.
3. Halide test- Add silver ions to identify the halide through the precipitate. Because the colours are so similar to further test it, add dilute aq ammonia if the precipitate dissolves it Cl, if it only dissolves in conc aq ammonia then it Br, if it doesn’t dissolve at all then it is iodine.

Question 20

Why is there a specific sequence for qualitative testing?

Answer 20

Carbonate ions must be first as neither halide or sulfates bubble in a dilute acid.
Sulphate must be after carbonate as Barium carbonates can also form a white precipitate making it harder to identify the ions, so make sure there is no carbonates before using this test.
Halide test must go last as Ag ions with carbonates and Sulphates can also both form precipitates, so its important to eliminate any possibilities of any other ions being present.

Question 21

How do you test if its one solution with a mixture of ions?

Answer 21

First do the carbonate test, but make sure that you continue to add dilute nitric acid until all the bubbling stops to ensure that all the carbonates have been removed.
Then when you’re doing the sulfate test make sure you use Barium nitrate and not barium chloride as that means chlorine ions will inevitably show up in the halide test. Make sure you add an excess of barium nitrate and to filter out all the barium nitrate.
Then lastly add AgNO3 [nitrate], therefore any precipitation here should just be halide ions. Then add dilute ammonia and if needed conc ammonia [aq].

Question 22

What is the test for cations/ ammonia gas?

Answer 22

When heated, aq ammonium ions and aq hydroxide ions react to form together and for ammonia gas NH3.
Therefore add aq NaOH to the solution of ammonium ion. Ammonia gas will be produced and released by warming the solution.
Use a moist pH indicator paper and the paper should turn blue.

Question 23

What is the difference between endothermic and exothermic?

Answer 23

Exothermic transfers energy (heat) from the system out to the surroundings.
Endothermic transfers energy from the surrounding to the system.

Question 24

What is activation energy?

Answer 24

Minimum energy required for a reaction to take place.

Question 25

What is enthalpy change of reaction?

Answer 25

The enthalpy change of a reaction in molar quantities shown in a chemical equation under standard conditions.

Question 26

What is enthalpy change of formation?

Answer 26

The enthalpy change of when one mole of compound is formed in standard conditions, with reactant and products in their standard states.

Question 27

What is enthalpy change of combustion?

Answer 27

Enthalpy change when one mole of a substance reacts completely with oxygen in standard conditions.

Question 28

What is the enthalpy change of neutralisation?

Answer 28

Enthalpy change when an acid and base react together to form one mole H2O.

Question 29

Energy change equation

Answer 29

q = m * c * change in temp

c = specific heat capacity = 4.18

Question 30

How to find enthalpy change from energy changes

Answer 30

Energy change divided by the mole.

Question 31

How accurate is the enthalpy change of combustion experiment?

Answer 31

• heat lost to the surrounding other than the water.
• incomplete combustion of methanol
• evaporation of methanol from the wick
• non-standard conditions could’ve been used.

Question 32

Exo or endo enthalpy changes?

Answer 32

Combustion = exo
Reaction + formation = exo or endo
Neutralisation= exo

Question 33

Equation for enthalpy change of reaction using bond enthalpies.

Answer 33

/IrH = sum of BEs in react - sum of BEs in prod

Question 34

Route for formation enthalpies

Answer 34

Route 1 = B + A
Route 2 = C
So by Hess’ law = A = C - B

Question 35

Formation routes for combustion.

Answer 35

Route 1 = A + C
Route 2 = B
Hess’ Law = A = B - C

Question 36

What is catalyst?

Answer 36

Provide an alternative reaction pathway of lower activation energy.
It is not used up in chemical reaction.
It is always regenerated in the end.
Homogenous Cat = Same physical state as the reactants to form an intermediate.
Heterogeneous Cat = Different physical state from the reactants. “Usually in solids in contact with gaseous reactants or reactants in solutions as they are dissolved and caused to react on the surface of the catalyst.

Question 37

Boltzmann distribution.

Answer 37

Question 38

BD with increase in temp

Answer 38

Question 39

BD with catalysts

Answer 39

Question 40

Features of dynamic equilibrium

Answer 40

Rate of forward reaction = to the rate of the reverse reaction.
Concentration of reactants and products do not change.
It is a closed system.

Question 41

What is Le Chatelier’s Principle?

Answer 41

Position of eqbm indicates the extent of the reaction.
Therefore if the temp, pressure or conc of the reactants of the products change then the position may change.
The principle states that when a system in eqbm externally changes then the system readjusts itself to minimise the effect of that change.

Question 42

What temp effect in equilibrium?

Answer 42

When temp increases = eqbm shifts towards the endothermic direction

When temp decrease = eqbm shifts towards the exothermic reaction.

Question 43

What is the Kc constant?

Answer 43

It is the eqbm constants that provide the actual position of the equilibrium.

If the Kc value is…
= 1, then the position is halfway btwn reactants and products.

> 1, then the position of equilibrium is towards the products.

<1, then the position is towards the reactants.