Module 3 - Periodic Table and Energy - Exam Questions

Question 1

Why does Xenon have a lower first ionisation energy than neon? (3)

Answer 1

Xe has a bigger atomic radius

Xe has more shielding so lower nuclear attraction

Question 2

Na melting point: 98°C

Mg melting point: 639°C

Explain the difference in melting point (3)

Answer 2

Mg ions have a greater charge

Mg has more electrons

Mg has greater attraction between ions and electrons

Question 3

Sulphur exists as S8 molecules, and chlorine as Cl2.

Explain why S has a higher melting point than Cl (2)

Answer 3

S8 and Cl2 have intermolecular forces

S8 has stronger intermolecular forces than Cl2

Question 4

Why does atomic radius decrease across a period? (3)

Answer 4

Nuclear charge increases

Shielding remains the same

Greater attraction

Question 5

Why does first ionisation energy increase across a period? (3)

Answer 5

Atomic radius decreases

Nuclear charge increases

Shielding remains the same

Question 6

Define first ionisation energy (3)

Answer 6

the energy required to remove one mole of electrons from one mole of gaseous atoms to form a +1 ion

Question 7

Explain why first ionisation energy of B is less than that of Be (2)

Answer 7

In B, electron being removed is at a higher energy

An s electron is lost in Be and a p electron is lost in B

Question 8

Explain why first ionisation energy of O is less than that of N (2)

Answer 8

In N, all 2p electrons are unpaired

In O, 2p electron removed is paired so has repulsion that makes removal easier.

Question 9

Describe what would be seen when a magnesium ribbon is added to excess dilute HCl (2)

Answer 9

Effervescence

Mg dissolves

Question 10

Describe the difference between Mg and Sr reacting with HCl (1)

Answer 10

Sr would be a quicker reaction

Question 11

Predict the formulas of: Barium oxide and barium nitride (2)

Answer 11

BaO

Ba3N2

Question 12

Describe and explain the trend down group 2 of reactivity with water (5)

Answer 12

Reactivity increases down the group

Atomic radii increase

More shielding

Nuclear attraction decreases

Easier to remove outer electrons

Question 13

A student reacts calcium exactly with HCl in solution. After adding more calcium it still reacts, explain this (2)

Answer 13

Calcium reacts with water producing calcium hydroxide

Ca(s) + H2O(l) -> Ca(OH)2(aq) + H2(g)

Question 14

Explain why samples of magnesium oxide become contaminated with magnesium carbonate over time (1)

Answer 14

MgO reacts with CO2

Question 15

CO2 can be prepared by which reaction of carbonates (1)

Answer 15

Thermal decomposition

Question 16

How do indigestion tablets containing CaCO3 work? (2)

Answer 16

CaCO3 neutralises HCl

CaCO3 + 2HCl → CaCl2 + H2O + CO2

Question 17

Write the equation and conditions for chlorine reacting with sodium hydroxide to form bleach (2)

Answer 17

2NaOH + Cl2 -> NaCl + NaClO + H2O

Cold and dilute NaOH

Question 18

Define disproportionation (1)

Answer 18

The simultaneous oxidation and reduction of the same element

Question 19

Which reagent would need to be added to calcium iodide to prove it contained iodide ions? (1)

Answer 19

Silver nitrate

Question 20

A solution contains CaBr2 and CaCl2, along with silver nitrate, which other reagent is added to prove iodide ions are present? (1)

Answer 20

Concentrated NH3

Question 21

Which reaction type is forming AgCl from adding silver nitrate to chloride ions? (1)

Answer 21

Precipitation

Question 22

Use bond breaking and bond making to explain why some reactions are exothermic (2)

Answer 22

Bond breaking absorbs energy and bond making releases energy

More energy released then absorbed

Question 23

Suggest three reasons why standard enthalpy changes of combustion are lower experimentally than theoretically (3)

Answer 23

Heat released to the surroundings

Incomplete combustion

Non-standard conditions

Question 24

Define enthalpy change of combustion (2)

Answer 24

the enthalpy change which occurs when one mole of the compound is burned completely in oxygen under standard conditions, and with everything in its standard state

Question 25

What are standard conditions? (1)

Answer 25

101kPa and 298K (25C)

Question 26

Why is it difficult to determine enthalpy change of formation for hydrocarbons? (1)

Answer 26

Many different hydrocarbons would form

Question 27

Why do bond enthalpies have positive values?

Answer 27

Bond breaking is endothermic

Question 28

Define enthalpy change of formation (2)

Answer 28

the change in enthalpy when one mole of a substance in the standard state is formed from its pure elements under the same conditions

Question 29

Define bond enthalpy (2)

Answer 29

Energy required to break 1 mole of bonds in the substance in the gaseous state

Question 30

Explain why increasing the temperature increases reaction rate (Boltzmann distribution) (1)

Answer 30

More molecules have energy above activation energy

Question 31

CO(g) + 2H2(g) -> CH3OH(g) ∆H = –91 kJ mol–1

Why would high pressure and low temperature give maximum yield? (2)

Answer 31

High pressure as fewer moles of gas on RHS

Low temperature as forward reaction is exothermic

Question 32

Why is high pressure and low temperature often not used in chemical industry for reaction conditions? (2)

Answer 32

Too expensive to use a high pressure

Too slow to use a low temperature

Question 33

Suggest two ways in which catalyst use in industry makes processes more sustainable (4)

Answer 33

Reactions take place at lower temperatures

Use less fossil fuel

Less CO2 emitted into atmosphere

Catalyst not used up in reaction

Question 34

State le Chatelier’s principle (2)

Answer 34

When a system in dynamic equilibrium is subjected to an external change, the system readjusts itself to minimise the effect of that change

Question 35

Describe the effect on equilibrium of adding a catalyst (2)

Answer 35

No change in equilibrium position

Catalyst speeds up forward and reverse reactions by same amount

Question 36

Give two features of a reversible reaction, when a dynamic equilibrium has been set up (2)

Answer 36

Rate of forward reaction = rate of reverse reaction

Concentrations remain constant

Question 37

What is meant by a catalyst? (1)

Answer 37

A substance that lowers the activation energy by providing an alternative route

Question 38

What is the difference between homogeneous and heterogeneous catalysts? (2)

Answer 38

Homogeneous: catalyst in same state as reactants

Heterogeneous: catalyst in different state to reactants

Question 39

State the pressure and temperature used in the Haber process (2)

Answer 39

Pressure: 200 atm

Temperature: 450°C

Question 40

Describe and explain why the conditions of the Haber process are a compromise between rate and equilibrium (9)

Answer 40

Increased pressure increases rate because molecules are closer together

Increased temperature increases rate because molecules have more energy

Increased pressure pushes equilibirum to RHS because fewer moles on RHS

Increased temperature pushes equilibrium to LHS because forward reaction is exothermic

If temperature is too high, yield is low

If temperature is too low, rate is slow

If pressure is too high, increased costs

Question 41

Answer 41

Question 42

Answer 42