AS AQA Chemistry Paper 2 2017 Questions
with Correct Answers
Explain why an increase in temperature increases the rate at which this gas
decomposes. [2 marks] - Correct Answer more molecules have sufficient energy to
react
this allows more successful collisions
Mass of X = 194 mg
Temperature = 373 K
Pressure = 102 kappa
Volume = 72 cm3
Calculate the relative molecular mass of X.
The gas constant, R = 8.31 J K−1 mol−1 - Correct Answer n = PV/RT
n= (102 𝑥 103 𝑥 72 𝑥 10−6) / (8.31 𝑥 373)
n= 0.0024
Mr. = mass / moles
Mr. = 0.194/0.0024
Mr. = 82
Analysis of a different hydrocarbon Y shows that it contains 83.7% by mass of
carbon.
Calculate the empirical formula of Y.
Use this empirical formula and the relative molecular mass of Y (Mr. = 86.0) to
calculate the molecular formula of Y. - Correct Answer dividing %s by relative
atomic masses C = 83.7/12(.0), H = 16.3/1
(C:H 6.975:16.3) = 3:7
Empirical formula = C3H7
Molecular formula = C6H14
Compounds A, B and C all have the molecular formula C5H10 A and B decolorize
bromine water but C does not.
B exists as two stereoisomers but A does NOT show stereoisomerism.
Use this information to deduce a possible structure for each of compounds A, B and
C and explain your deductions.
State the meaning of the term stereoisomers and explain how they arise in
compound B. - Correct Answer A & B are unsaturated
as they decolorize bromine water
, C is saturated
as it does not decolorize bromine water
A structures could be pent-1-ene
B structure could be pent-2-ene
C structure could be cyclopentane
stereoisomerism has the same structural formula but a different arrangement of
atoms in space
C=C cannot rotate
It arises by discussing that each C in C=C has two different groups
When alkanes are burned in an excess of oxygen they produce carbon dioxide and
water.
Write an equation for the complete combustion of propane in oxygen - Correct
Answer C3H8 + 5O2 = 3CO2 + 4H2O
An expression can be derived using bond enthalpy data to estimate the enthalpy of
combustion (∆chi) of an alkane.
For an alkane with n carbon atoms: ∆chi = - (496n + 202) kJ mol−1
The enthalpy of combustion of an alkane was calculated to be -6650 kJ mol−1 using
this expression.
Deduce the molecular formula of this alkane. Show your working. - Correct Answer
-6650 = -(496n + 202)
496n = 6650 - 202
496n = 6448
(n = 13)
C13H28
Suggest ONE reason, other than the use of mean bond enthalpies, why a value for
the enthalpy of combustion of a liquid alkane is different from C13H28 - Correct
Answer It takes energy to convert it into a gas
Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in cars.
When isooctane is burned, the enthalpy change is −47.8 kJ g−1
Isooctane is a liquid at room temperature with a density of 0.692 g cm−3
Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in
excess oxygen. - Correct Answer mass of isooctane = 692 (g)
33100 (kJ)
with Correct Answers
Explain why an increase in temperature increases the rate at which this gas
decomposes. [2 marks] - Correct Answer more molecules have sufficient energy to
react
this allows more successful collisions
Mass of X = 194 mg
Temperature = 373 K
Pressure = 102 kappa
Volume = 72 cm3
Calculate the relative molecular mass of X.
The gas constant, R = 8.31 J K−1 mol−1 - Correct Answer n = PV/RT
n= (102 𝑥 103 𝑥 72 𝑥 10−6) / (8.31 𝑥 373)
n= 0.0024
Mr. = mass / moles
Mr. = 0.194/0.0024
Mr. = 82
Analysis of a different hydrocarbon Y shows that it contains 83.7% by mass of
carbon.
Calculate the empirical formula of Y.
Use this empirical formula and the relative molecular mass of Y (Mr. = 86.0) to
calculate the molecular formula of Y. - Correct Answer dividing %s by relative
atomic masses C = 83.7/12(.0), H = 16.3/1
(C:H 6.975:16.3) = 3:7
Empirical formula = C3H7
Molecular formula = C6H14
Compounds A, B and C all have the molecular formula C5H10 A and B decolorize
bromine water but C does not.
B exists as two stereoisomers but A does NOT show stereoisomerism.
Use this information to deduce a possible structure for each of compounds A, B and
C and explain your deductions.
State the meaning of the term stereoisomers and explain how they arise in
compound B. - Correct Answer A & B are unsaturated
as they decolorize bromine water
, C is saturated
as it does not decolorize bromine water
A structures could be pent-1-ene
B structure could be pent-2-ene
C structure could be cyclopentane
stereoisomerism has the same structural formula but a different arrangement of
atoms in space
C=C cannot rotate
It arises by discussing that each C in C=C has two different groups
When alkanes are burned in an excess of oxygen they produce carbon dioxide and
water.
Write an equation for the complete combustion of propane in oxygen - Correct
Answer C3H8 + 5O2 = 3CO2 + 4H2O
An expression can be derived using bond enthalpy data to estimate the enthalpy of
combustion (∆chi) of an alkane.
For an alkane with n carbon atoms: ∆chi = - (496n + 202) kJ mol−1
The enthalpy of combustion of an alkane was calculated to be -6650 kJ mol−1 using
this expression.
Deduce the molecular formula of this alkane. Show your working. - Correct Answer
-6650 = -(496n + 202)
496n = 6650 - 202
496n = 6448
(n = 13)
C13H28
Suggest ONE reason, other than the use of mean bond enthalpies, why a value for
the enthalpy of combustion of a liquid alkane is different from C13H28 - Correct
Answer It takes energy to convert it into a gas
Isooctane (2,2,4-trimethylpentane) is an important component of petrol used in cars.
When isooctane is burned, the enthalpy change is −47.8 kJ g−1
Isooctane is a liquid at room temperature with a density of 0.692 g cm−3
Calculate the heat energy released, in kJ, when 1.00 dm3 of isooctane burns in
excess oxygen. - Correct Answer mass of isooctane = 692 (g)
33100 (kJ)
