Exam q's

Question 1

Ethane-1,2-diol can be dissolved in water to act as an anti-freeze in car radiators.
Explain why ethane-1,2-diol is very soluble in water.

Answer 1

Because it has polar O-H bonds which form hydrogen bonds with water molecules.

Question 2

Module three: What is the equation for the third ionisation energy of magnesium?

Answer 2

Mg2+(g) → Mg3+(g) + e–

Question 3

Module three: which successive ionisation energy is being described?
The energy required to remove one electron from each ion in one mole of gaseous 4+ ions.

Answer 3

The fifth ionisation energy. (as the fifth electron is being removed)

Question 4

Module three: Solid graphite and iodine contain covalent bonds but their melting points and electrical conductivities are very different. Explain the difference in melting points and electrical conductivities.

Answer 4

Graphite has a giant covalent lattice and iodine has a simple molecular lattice

On melting, covalent bonds are broken in graphite

London forces are broken between iodine molecules

Covalent bonds are much stronger

Covalent bonds require more energy input to break and graphite has a much higher melting point

Question 5

Module three: Define the term first ionisation energy.

Answer 5

The energy required to remove one electron from each atom in one mole
of gaseous atoms

Question 6

Module three: Explain why first ionisation energies show a general increase across period three.

Answer 6

Across Period 3, nuclear charge increases because there are more protons. Electrons are added to the same shell
and attraction between nucleus and outer electrons increases.

Question 7

Module three: Explain why the first ionisation energy of B is less than that of Be

Answer 7

In B, electron is removed from a 2p orbital rather than 2s orbital in Be. The 2p sub-shell is at higher energy and its electron is easier to remove

Question 8

Module three: Explain why the first ionisation energy of O is less than that of N?

Answer 8

In O, one of the 2p orbitals contains paired electrons whereas in N, all three orbitals are singly occupied. The paired electrons in O repel and electron is easier to remove.

Question 9

Module three: State and explain the trend in first ionisation energies going down the first three elements of the noble gases?

Answer 9

Down a group, electrons are added to a new shell, further from the nucleus

There are more inner shells between the outer electrons and the nucleus, increasing the shielding

Attraction between nucleus and outer electrons decreases so the first ionisation energy decreases.

Question 10

Module three: What is the equation for the fourth ionisation energy of nitrogen?

Answer 10

N3+(g) → N4+(g) + e–

Question 11

Module three: Suggest why the successive ionisation energies of Nitrogen increase in value?

Answer 11

As each electron is removed the remaining electrons are attracted more to the nucleus

Question 12

Module three: What do large differences between successive ionisation energies indicate?

Answer 12

Large differences between successive ionisation energies indicate a different shell which is closer to nucleus.

Question 13

Module three: Why do metallic lattices conduct electricity and why do ionic lattices only conduct electricity when they are molten/melted?

Answer 13

Giant metallic lattice has mobile electrons.

The giant ionic lattice has no mobile ions as all ions are fixed in position.

When molten, the ionic lattice collapses and the ions are now able to move and conduct electricity Giant metallic lattice has mobile electrons.

The giant ionic lattice has no mobile ions as all ions are fixed in position.

When molten, the ionic lattice collapses and the ions are now able to move and conduct electricity

Question 14

Module three: Why does SiO2 melt at such a higher temperature than SiCl4?

Answer 14

SiO2 has a giant covalent lattice structure.
SiCl4 has a simple molecular lattice structure.
For melting, strong covalent bonds are broken in SiO2.
Weak London forces are broken in SiCl4
More energy is required to break stronger forces in SiO2 than SiCl4

Question 15

Module three: What is meant by metallic bonding?

Answer 15

Attraction between positive ions and delocalised electrons.

Question 16

Module three: Explain why the melting point of phosphorus is higher than that of chlorine?

Answer 16

Sulfur exists as S8 and chlorine as Cl2 molecules.

London forces are stronger between S8 molecules as they have more electrons than Cl2 molecules

Question 17

Module three: What is meant by disproportionation?

Answer 17

Disproportionation is the simultaneous oxidation and reduction of the same element in the same redox reaction.

Question 18

Module three: Write a half equation to show the reduction of chlorine. (When it reduces from 0 to -2)

Answer 18

Cl2 + 2e– → 2Cl–

Question 19

Module three: If a reaction is done with bromine instead of chlorine what is likely to happen?

Answer 19

The rate of reaction would be slower because bromine is less reactive that chlorine.

Question 20

Module three: Explain in terms of first ionisation energy the trend in reactivity going down group 2.

Answer 20

Down a group, electrons are added to a new shell, further from the nucleus

There are more inner shells between the outer electrons and the nucleus, increasing the shielding

Attraction between nucleus and outer electrons decreases

Therefore less energy is required to lose an electron and reactivity of Group 2 increases

Question 21

Module three: What compound of magnesium can be used to treat heartburn?

Answer 21

Magnesium carbonate, hydroxide or oxide

Question 22

Module three: Define the term standard enthalpy change of formation (include the standard conditions in your answer)

Answer 22

standard enthalpy change of formation is the enthalpy change for the formation of 1 mole

of a substance from its constituent elements

under standard conditions of 100 kPa and 298 K

Question 23

Module three: Define the term standard enthalpy change of combustion (include the standard conditions in your answer)

Answer 23

The enthalpy change from the complete combustion

of 1 mole

of a substance under standard conditions of 100 kPa and 298 K

Question 24

Module three: What does a Kc value greater than 1 indicate?

Answer 24

It indicates a position of equilibrium that is towards the products.

Question 25

Module three: What does a Kc value less than 1 indicate?

Answer 25

It indicates a position of equilibrium that is towards the reactants.

Question 26

Module three: What does a larger value of Kc indicate?

Answer 26

The larger the Kc value, the further the position of equilibrium lies to the right and greater the concentrations of the products compared to the reactants.

Question 27

Module three: What’s the difference between a homogenous and heterogeneous catalyst?

Answer 27

A homogeneous catalyst has the same physical state as the reactants, whereas a heterogeneous catalyst has a different physical state from the reactants.

Question 28

Module three: How does a homogeneous catalyst work?

Answer 28

The catalyst reacts with the reactants to form an intermediate then breaks down to give the product and regenerates the catalyst.

Question 29

Module three: How does a heterogenous catalyst work?

Answer 29

They’re usually solids in contact with gaseous reactants or reactants in solution. Reactant molecules are adsorbed (weakly bonded) onto the surface of the catalyst, where the reaction takes place. After the reaction, the product molecules leave the surface of the catalyst by desorption.

Question 30

Module three: What effect does increasing/decreasing the temperature have on the position of equilibrium?

Answer 30

Increasing temperature shifts equilibrium in the endothermic direction. Decreasing temperature shifts the position of equilibrium in the exothermic direction (delta H negative).

Question 31

Module three: What effect does increasing/decreasing the pressure have on the position of equilibrium?

Answer 31

Increasing pressure shifts equilibrium towards fewer gaseous molecules. Decreasing pressure shifts equilibrium towards more gaseous molecules.

Question 32

Module three: What effect does a catalyst have on equilibrium?

Answer 32

Doesn’t change the position of equilibrium, merely speeds up both forwards and reverse reactions equally. It increasing the rate at which an equilibrium is established.