Module 3

Question 1

Why are group 1 & 2 elements classified as s-block elements?

Answer 1

Their highest energy electron(s) are in an s-orbital or sub-shell.

Question 2

Why can elements be classified as p-block elements?

Answer 2

Their highest energy electron(s) are in a p-orbital or sub-shell.

Question 3

Why can elements be classified as a d-block element?

Answer 3

Their highest energy electron(s) are in a d-orbital or sub-shell.

Question 4

What is meant by the term first ionisation energy?

Answer 4

The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions.

Question 5

What are the three factors that affect ionisation energy?

Answer 5

• atomic radius
• nuclear charge
• electron shielding

Question 6

What is the general trend in ionisation energy across a period? Explain why.

Answer 6

- ionisation energy increases
Due to:
- atomic radii decrease
- increase in nuclear charge
- increase in nuclear attraction

Question 7

What is the general trend in ionisation energy down a group? Explain why.

Answer 7

- ionisation energy decreases
Due to:
- increase in atomic radii
- increase in electron shielding
- decrease in nuclear attraction
* increase in nuclear charge is outweighed!

Question 8

Why is there a small decrease in ionisation energy between elements in group 2 to 3?

Answer 8

• group 3 elements have outer electron in a p-orbital, slightly further from the nucleus and easier to remove

Question 9

Why is there a small decrease in ionisation energy between elements in group 5 to 6?

Answer 9

• group 6 elements start to have their electrons spin-pair, small repulsion between paired electrons and easier to remove

Question 10

What is meant by the term metallic bonding?

Answer 10

Electrostatic force of attraction between positive metal ions and delocalised electrons.

Question 11

What is the trend in reactivity down group 2? Explain why.

Answer 11

• reactivity increases

- atomic radius increases and electron shielding increases, electrons easier to remove

Question 12

What is the trend in solubility down group 2? What is the effect on pH?

Answer 12

• solubility increases

- resulting solutions are more alkaline, higher pH

Question 13

What is calcium hydroxide used for?

Answer 13

“Lime” to neutralise acidic soil

Question 14

What is magnesium hydroxide used for?

Answer 14

Milk of magnesia to neutralise excess stomach acid

Question 15

What is calcium carbonate used for?

Answer 15

Limestone as a building material

Question 16

What is the limitation for the use of calcium carbonate in buildings and statues?

Answer 16

Reacts with acids in rainwater leading to erosion

Question 17

What is the trend in boiling points down group 7? Explain why.

Answer 17

• increase

- London forces increase with increasing number of electrons

Question 18

What is the trend in reactivity down group 7? Explain why.

Answer 18

• decreases
• increase in atomic radius
• increase in electron shielding
• ability to gain electron decreases due to increased repulsion

Question 19

What is meant by the term disproportionation?

Answer 19

The oxidation and reduction of the same element in a redox reaction.

Question 20

What colour is chlorine in both water and cyclohexane?

Answer 20

Pale green in both

Question 21

What colour is bromine in both water and cyclohexane?

Answer 21

Orange in both

Question 22

What colour is iodine in water and cyclohexane?

Answer 22

Brown in water

Violet in cyclohexane

Question 23

Why is chlorine used to treat drinking water?

Answer 23

Kills bacteria, makes it safe to drink

Question 24

What are the disadvantages of using chlorine to treat drinking water?

Answer 24

Possible source of toxic chlorine gas, risk of forming chlorinated hydrocarbons

Question 25

What are the results of testing for the haloed ions using silver nitrate solution?

Answer 25

``` Chloride = white precipitate Bromide = cream precipitate Iodide = yellow precipitate ```

Question 26

What are the results of testing the precipitates formed from the reaction of halide ions with silver nitrate solution when tested with ammonia?

Answer 26

- Dilute ammonia - White precipitate dissolves - Conc. ammonia - cream precipitate dissolves - yellow precipitate will not dissolve on addition of ammonia

Question 27

What is meant by the term activation energy?

Answer 27

The minimum energy required to start a reaction by breaking bonds in the reactants.

Question 28

What are the standard conditions?

Answer 28

100 kPa 298 K Solutions 1 mol/dm3

Question 29

What is meant by the term enthalpy change of formation?

Answer 29

The energy change that takes place when one mole of a compound is formed from its constituent elements in their standard states under standard conditions.

Question 30

What is meant by the term enthalpy change of combustion?

Answer 30

The energy change that takes place when one mole of a substance is completely combusted.

Question 31

What is meant by the term enthalpy change of neutralisation?

Answer 31

The energy change associated with the formation of one mole of water from a neutralisation reaction, under standard conditions.

Question 32

Why might the value for average bond enthalpy differ from the actual bond enthalpy?

Answer 32

The same bond in a different species may require a different amount of energy to break it, the average takes into account all different values for that type of bond.

Question 33

How is the Periodic Table arranged?

Answer 33

- by increasing atomic number - in periods showing repeating trends in physical and chemical properties - in groups having similar chemical properties

Question 34

What are the factors that affect rate of reaction?

Answer 34

- temperature - pressure (gas only) - concentration - surface area - catalysts

Question 35

How do an increase in pressure or concentration result in an increase in the rate of a reaction?

Answer 35

FESC = more particles, more frequent collisions, more successful collisions, faster rate

Question 36

How can reactions be monitored in order to calculate their rate of reaction?

Answer 36

- collecting volume of gas - measuring mass throughout - time taken for visible change - colorimeter to measure conc.

Question 37

What is meant by the term catalyst?

Answer 37

A substance that increases the rate of reaction without being used up during the process (it is regenerated). Provides an alternative pathway with a lower activation energy.

Question 38

What is meant by the term homogeneous catalyst?

Answer 38

A catalyst used in a reaction which is in the same phase as the reactant.

Question 39

What is meant by the term heterogeneous catalyst?

Answer 39

A catalyst used in a reaction which is in a different phase from the reactant.

Question 40

What are the advantages of using catalysts?

Answer 40

- lower energy demands - reduce costs of processes - better for environment, less fossil fuels burned - lower carbon dioxide emissions

Question 41

What are the disadvantages of using catalysts?

Answer 41

- can contain toxic substances - hard/costly to obtain - may still require high pressures and temps.

Question 42

What are the key features of the Boltzmann distribution?

Answer 42

- area under curve = total number of molecules (constant) - no molecules with no energy (starts at origin) - no maximum energy (does not touch x axis) - only molecules with energy greater than Ea will react

Question 43

What is meant by the term dynamic equilibrium?

Answer 43

The equilibrium that exists in a closed system when the rate of the forward reaction is equal to the rate of the reverse reaction and all the chemicals have their concentrations maintained.

Question 44

What happens to the position of equilibrium when the concentration is increased?

Answer 44

Equilibrium will shift to use excess (away from increase)

Question 45

What happens to the position of equilibrium when the concentration is decreased?

Answer 45

Equilibrium will shift to replace the decrease (shifts towards change)

Question 46

What will happen to the position of equilibrium if temperature is increased?

Answer 46

Shifts towards endothermic side

Question 47

What happens to the position of equilibrium when temperature is decreased?

Answer 47

Shifts towards exothermic side

Question 48

What happens to the position of equilibrium when pressure is increased?

Answer 48

Shifts towards side with fewest moles of gas

Question 49

What happens to position of equilibrium when pressure is decreased?

Answer 49

Shifts towards side with most moles of gas

Question 50

Why do catalysts have no effect on position of equilibrium?

Answer 50

Speed up rate of both forward and reverse reactions by the same amount

Question 51

What can be concluded about the position of equilibrium if the value of Kc is large?

Answer 51

Favours product side

Question 52

What can be concluded about the position of equilibrium if the value of Kc is small?

Answer 52

Favours reactant side