exam questions - paper 1 (a-level)

Question 1

Define the term enthalpy of lattice formation.

Answer 1

enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions.

Question 2

Explain why some lattice formation values may differ from theoretical values.

Answer 2

• ionic model assumes perfect ionic bonding
• a difference in values suggests that lattice is not purely ionic i.e may contain covalent character

Question 3

Gibbs Free Equation

Answer 3

ΔG = ΔH - TΔS

Question 4

equation for ΔS

Answer 4

products - reactants

Question 5

Give an equation to present the process of electrospray ionisation.

Answer 5

X + H⁺ → XH⁺

Question 6

Explain how a heterogeneous catalyst works.

Answer 6

1) reactants adsorb onto the catalyst surface
2) reaction occurs on surface (bonds weaken)
3) desorption of products (break away from surface)

Question 7

Explain why isotopes have identical chemical properties.

Answer 7

due to same electronic configuration

Question 8

Explain how a salt bridge provides an electrical connection between two
solutions.

Answer 8

it has free ions that can move through it

Question 9

How do you calculate electrode potential?

Answer 9

Eꝋ(cell) = Eꝋ(red) - Eꝋ(ox)

(more positive - less positive)

Question 10

State how electrode cells are represented, include state symbols.

Answer 10

X (s) | X²⁺ (aq) || Y²⁺ (aq) | Y (s)

x = reducing agent (most negative)
y = oxidising agent (most positive)

Question 11

Define the term enthalpy of lattice dissociation.

Answer 11

enthalpy change when 1 mole of an ionic compound is dissociated into its component ions in the gaseous state

Question 12

In terms of forces, explain why the first electron affinity of oxygen is an exothermic process.

Answer 12

there is an attractive force between the nucleus of oxygen & an external e-

Question 13

Define the term enthalpy of hydration.

Answer 13

enthalpy change when 1 mole of gaseous ions dissolve in sufficient water to form 1 mol of aqueous ions and give an infinitely dilute solution

Question 14

Define the term enthalpy of solution.

Answer 14

enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution

Question 15

Explain why adding a catalyst has no effect on the value of Kp.

Answer 15

catalyst increases rate of forward reaction and backward reaction by the same amount

Question 16

Conditions for standard hydrogen electrode.

Answer 16

→ hydrogen gas 100kPa
→ solution with hydrogen ion at 1.0 mol dm^-3
→ temperature at 298K
→ platinum electrode

Question 17

In terms of electrostatic forces, suggest why the electron affinity of fluorine has a negative value.

Answer 17

→ attraction between nucleus and electron
→ releases energy

Question 18

Give two reasons why it is necessary to ionise a sample before they can be analysed in a TOF mass spectrometer.

Answer 18

→ Ions can be accelerated by an electric field
→ Ions create a current when hitting the detector

Question 19

Explain the effect of a catalyst on Kp.

Answer 19

→ no effect
→ increases rate of forward and backward reaction
equally/by the same amount

Question 20

State the meaning of the term enthalpy change.

Answer 20

heat change at constant pressure

Question 21

Suggest why the enthalpy of hydration of calcium is less exothermic than magnesium

Answer 21

→ Ca2+ (ion) bigger than Mg2+
→ weaker attraction to Oδ- in water

Question 22

Describe the structure and bonding of P4O10

Answer 22

→ P4O10 is a simple covalent molecule
→ weak van der Waals forces between molecules

Question 23

Describe the factors that affect the efficiency and lifetime of the catalyst.

Answer 23

→ large surface area increases efficiency
→ catalyst poisoned/ blocked active sites

Question 24

State the meaning of the term electrochemical series.

Answer 24

list of electrode potentials in (numerical) order

Question 25

Explain qualitatively why raising the temperature by 10°C has a much greater effect on rate of reaction than doubling the concentration

Answer 25

→ reaction occurs when molecules have E≥Ea
→ raising T by 10 °C causes many more molecules to have this E
→ whereas doubling [x] only doubles the number with this E

Question 26

Explain why increasing temperature increases Kw.

Answer 26

→ dissociation is endothermic
→ ∴ equilibrium moves to RHS to oppose increase in T

Question 27

Give the meaning of the term dynamic in the context of a dynamic equilibrium

Answer 27

forward and reverse reactions occur at the same time

Question 28

In a mass spectrum. state which ions produce the biggest current at the detector.

Answer 28

the most abundant one

Question 29

Explain why chloroethanoic acid is a stronger acid than ethanoic acid.

Answer 29

→ chlorine withdraws electrons as it is electronegative

Question 30

Explain why chloroethanoic acid is a stronger acid than ethanoic acid.

Answer 30

→ chlorine withdraws electrons as it is electronegative
→ reduces charge on COO-
→ weakens O-H bond

Question 31

Define the term electron affinity.

Answer 31

enthalpy change when one mole of negative ions are formed from one mole of atoms with all ions and atoms in the gaseous state