alkanes

Question 1

Which is a propagation step in the chlorination of methane?
A H● + Cl2 → HCl + Cl●
B Cl● + CH4 → CH3Cl + H●
C ● CH3 + Cl● → CH3Cl
D ● CH3 + Cl2 → CH3Cl + Cl●

Answer 1

D
*CH3 + Cl2 → CH3Cl + Cl

Question 2

Which correctly represents an incomplete combustion of pentane?
A C5H12 + 8O2 ⟶ 5CO2 + 6H2O
B C5H12 + 8O2 ⟶ 4CO + CO2 + 6H2O
C C5H12 + 6O2 ⟶ 4CO + CO2 + 6H2O
D C5H12 + 5O2 ⟶ 4CO + CO2 + 4H2O + 2H2

Answer 2

c

Has to be balanced even if incompletely combusted

Question 3

Which species is produced in a propagation step during the reaction of propane
with an excess of chlorine in the presence of UV light?
A H*
B C3H5Cl
C C3H6CL2
D C6H14

Answer 3

c

Question 4

Sulfur dioxide (SO2) is produced when some fossil fuels are burned.
Which of the following statements is true?
A Sulfur dioxide can be removed from waste gases in a
power station by an acid-base reaction with calcium oxide.
B Sulfur dioxide is insoluble in water.
C Sulfur dioxide is a basic oxide.
D Sulfur dioxide is an ionic compound.

Answer 4

A

Question 5

The combustion of petrol in car engines produces the pollutant nitrogen
monoxide.
Give an equation for a reaction that removes nitrogen monoxide in a
catalytic converter.

Answer 5

2 NO + 2 CO → N2 + 2 CO2

2NO → N2 + O2 (or multiples)

Question 6

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 the
value obtained using the expression in part (b

Answer 6

alkane is not gaseous or
* equation relates to gaseous alkanes or
* it takes energy to convert it into a gas or
* that water / alkane / substances are gaseous in calculations using
bond enthalpies

Question 8

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.
Give your answer to the appropriate number of significant figures.

Answer 8

mass of isooctane = 692 (g)
correct answer scores M1 and M2
1
M2 3.31 × 104 or 33100 (kJ) (3sf only)