exam questions - paper 1 (a-level) Flashcards
Define the term enthalpy of lattice formation.
enthalpy change when 1 mole of solid ionic compound is formed from its gaseous ions.
Explain why some lattice formation values may differ from theoretical values.
- ionic model assumes perfect ionic bonding
- a difference in values suggests that lattice is not purely ionic i.e may contain covalent character
Gibbs Free Equation
ΔG = ΔH - TΔS
equation for ΔS
products - reactants
Give an equation to present the process of electrospray ionisation.
X + H⁺ → XH⁺
Explain how a heterogeneous catalyst works.
1) reactants adsorb onto the catalyst surface
2) reaction occurs on surface (bonds weaken)
3) desorption of products (break away from surface)
Explain why isotopes have identical chemical properties.
due to same electronic configuration
Explain how a salt bridge provides an electrical connection between two
solutions.
it has free ions that can move through it
How do you calculate electrode potential?
Eꝋ(cell) = Eꝋ(red) - Eꝋ(ox)
(more positive - less positive)
State how electrode cells are represented, include state symbols.
X (s) | X²⁺ (aq) || Y²⁺ (aq) | Y (s)
x = reducing agent (most negative)
y = oxidising agent (most positive)
Define the term enthalpy of lattice dissociation.
enthalpy change when 1 mole of an ionic compound is dissociated into its component ions in the gaseous state
In terms of forces, explain why the first electron affinity of oxygen is an exothermic process.
there is an attractive force between the nucleus of oxygen & an external e-
Define the term enthalpy of hydration.
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
Define the term enthalpy of solution.
enthalpy change when 1 mole of an ionic substance dissolves in water to give a solution of infinite dilution
Explain why adding a catalyst has no effect on the value of Kp.
catalyst increases rate of forward reaction and backward reaction by the same amount
Conditions for standard hydrogen electrode.
→ hydrogen gas 100kPa
→ solution with hydrogen ion at 1.0 mol dm^-3
→ temperature at 298K
→ platinum electrode
In terms of electrostatic forces, suggest why the electron affinity of fluorine has a negative value.
→ attraction between nucleus and electron
→ releases energy
Give two reasons why it is necessary to ionise a sample before they can be analysed in a TOF mass spectrometer.
→ Ions can be accelerated by an electric field
→ Ions create a current when hitting the detector
Explain the effect of a catalyst on Kp.
→ no effect
→ increases rate of forward and backward reaction
equally/by the same amount
State the meaning of the term enthalpy change.
heat change at constant pressure
Suggest why the enthalpy of hydration of calcium is less exothermic than magnesium
→ Ca2+ (ion) bigger than Mg2+
→ weaker attraction to Oδ- in water
Describe the structure and bonding of P4O10
→ P4O10 is a simple covalent molecule
→ weak van der Waals forces between molecules
Describe the factors that affect the efficiency and lifetime of the catalyst.
→ large surface area increases efficiency
→ catalyst poisoned/ blocked active sites
State the meaning of the term electrochemical series.
list of electrode potentials in (numerical) order
Explain qualitatively why raising the temperature by 10°C has a much greater effect on rate of reaction than doubling the concentration
→ 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
Explain why increasing temperature increases Kw.
→ dissociation is endothermic
→ ∴ equilibrium moves to RHS to oppose increase in T
Give the meaning of the term dynamic in the context of a dynamic equilibrium
forward and reverse reactions occur at the same time
In a mass spectrum. state which ions produce the biggest current at the detector.
the most abundant one
Explain why chloroethanoic acid is a stronger acid than ethanoic acid.
→ chlorine withdraws electrons as it is electronegative
Explain why chloroethanoic acid is a stronger acid than ethanoic acid.
→ chlorine withdraws electrons as it is electronegative
→ reduces charge on COO-
→ weakens O-H bond
Define the term electron affinity.
enthalpy change when one mole of negative ions are formed from one mole of atoms with all ions and atoms in the gaseous state
