AQA A-LEVEL CHEMISTRY EXAM QUESTIONS
AND ANSWERS WITH ACCURATE
RATIONALES(PASSED).
Define the term standard enthalpy of combustion. -
correct 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.
Describe the steps you would take to determine an
accurate minimum temperature that is not influenced
from heat from the surroundings. - correct 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
Explain how oxides of nitrogen are formed during the
combustion of alkanes. - correct answer - -nitrogen and
oxygen in the air
-react at high temperatures to form NO, NO2 etc.
, Explain what is meant by the term fraction as applied to
fractional distillation. - correct answer - a group of
molecules with similar boiling points / similar chain length
Explain why CF4 has a bond angle of 109.5°. - correct
answer - -there are 4 bonding pairs and no lone pairs
-repel equally and therefore spread apart as far as
possible
Explain why ethanoic anhydride might be preferable to
use when making N-phenylethanamide, although it has a
slower rate of reaction. - correct answer - -it has a
violent reaction with water
-produces toxic HCl gas
Explain why the catalyst in a catalytic converter is coated
on a honeycomb. - correct answer - -increases surface
area
-increases rate of reaction
Explain why the melting point of dodecane is higher than
the melting point of the straight-chain alkane produced
by cracking dodecane. - correct answer - -larger
molecule with more electrons
-more and stronger van der Waals' forces
AND ANSWERS WITH ACCURATE
RATIONALES(PASSED).
Define the term standard enthalpy of combustion. -
correct 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.
Describe the steps you would take to determine an
accurate minimum temperature that is not influenced
from heat from the surroundings. - correct 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
Explain how oxides of nitrogen are formed during the
combustion of alkanes. - correct answer - -nitrogen and
oxygen in the air
-react at high temperatures to form NO, NO2 etc.
, Explain what is meant by the term fraction as applied to
fractional distillation. - correct answer - a group of
molecules with similar boiling points / similar chain length
Explain why CF4 has a bond angle of 109.5°. - correct
answer - -there are 4 bonding pairs and no lone pairs
-repel equally and therefore spread apart as far as
possible
Explain why ethanoic anhydride might be preferable to
use when making N-phenylethanamide, although it has a
slower rate of reaction. - correct answer - -it has a
violent reaction with water
-produces toxic HCl gas
Explain why the catalyst in a catalytic converter is coated
on a honeycomb. - correct answer - -increases surface
area
-increases rate of reaction
Explain why the melting point of dodecane is higher than
the melting point of the straight-chain alkane produced
by cracking dodecane. - correct answer - -larger
molecule with more electrons
-more and stronger van der Waals' forces
