AQA A-Level Chemistry Exam
Questions
Topic 1 - Answer-Atomic Structure
Topic 2 - Answer-Amount of Substance
State what is meant by the term molecular formula. - Answer-the actual no. atoms of each element in a
compound
Topic 3 - Answer-Bonding
Explain why CF4 has a bond angle of 109.5°. - Answer--there are 4 bonding pairs and no lone pairs
-repel equally and therefore spread apart as far as possible
Topic 4 - Answer-Energetics
State and explain change in the volume of water in calorimetry that would cause a reduction in heat
loss. - Answer--higher volume
-smaller increase in temperature above room temperature / increased contact with calorimetry /
smaller heat loss by evaporation
Define the term standard enthalpy of combustion. - Answer-The enthalpy change when one mole of a
substance is burnt completely in oxygen under standard conditions with all reactants and products in
their standard states.
, State why experimental values for enthalpy change is different to mean bond enthalpy. - Answer--heat
loss / not all heat transferred to apparatus
-reactants and products may not be in their standard states
-MBE values are taken from a range of compounds
-incomplete combustion
-water may end up in a gaseous state
-MBE refers to gaseous species whereas enthalpy change of combustion is liquid species
Give the meaning of the term mean bond enthalpy. - Answer-Enthalpy for dissociating covalent bonds,
averaged for that bond type for a range of values.
Describe the steps you would take to determine an accurate minimum temperature that is not
influenced from heat from the surroundings. - Answer--start clock when compound is added
-record every minute for 5 minutes
-plot temperature vs time graph
-extrapolate time back to the time of mixing to determine the temperature
Topic 5 - Answer-Kinetics
Suggest why a catalyst used in a process may become less efficient if the reactants contain impurities. -
Answer-Impurities block the active site.
Topic 6 - Answer-Chemical Equilibria, Le Châtelier's principle and Kc
Topic 7 - Answer-Oxidation, Reduction and Redox Equations
Questions
Topic 1 - Answer-Atomic Structure
Topic 2 - Answer-Amount of Substance
State what is meant by the term molecular formula. - Answer-the actual no. atoms of each element in a
compound
Topic 3 - Answer-Bonding
Explain why CF4 has a bond angle of 109.5°. - Answer--there are 4 bonding pairs and no lone pairs
-repel equally and therefore spread apart as far as possible
Topic 4 - Answer-Energetics
State and explain change in the volume of water in calorimetry that would cause a reduction in heat
loss. - Answer--higher volume
-smaller increase in temperature above room temperature / increased contact with calorimetry /
smaller heat loss by evaporation
Define the term standard enthalpy of combustion. - Answer-The enthalpy change when one mole of a
substance is burnt completely in oxygen under standard conditions with all reactants and products in
their standard states.
, State why experimental values for enthalpy change is different to mean bond enthalpy. - Answer--heat
loss / not all heat transferred to apparatus
-reactants and products may not be in their standard states
-MBE values are taken from a range of compounds
-incomplete combustion
-water may end up in a gaseous state
-MBE refers to gaseous species whereas enthalpy change of combustion is liquid species
Give the meaning of the term mean bond enthalpy. - Answer-Enthalpy for dissociating covalent bonds,
averaged for that bond type for a range of values.
Describe the steps you would take to determine an accurate minimum temperature that is not
influenced from heat from the surroundings. - Answer--start clock when compound is added
-record every minute for 5 minutes
-plot temperature vs time graph
-extrapolate time back to the time of mixing to determine the temperature
Topic 5 - Answer-Kinetics
Suggest why a catalyst used in a process may become less efficient if the reactants contain impurities. -
Answer-Impurities block the active site.
Topic 6 - Answer-Chemical Equilibria, Le Châtelier's principle and Kc
Topic 7 - Answer-Oxidation, Reduction and Redox Equations
