2012 Chains, Energy and Resources Jun

Question 1

Explain why crude oil can be separated into different fractions

Answer 1

• Because hydrocarbons have different boiling points

Question 2

Explain why a variety of alkanes and alkenes are formed with different chain lengths

Answer 2

• Carbon-Carbon bonds can break anywhere

Question 3

Describe how ethene can be converted into 1,2-dibromoethane, bromoethane and ethanol

Name and describe the mechanism for the conversion of ethene into 1,2-dibromoethane

Answer 3

• React with bromine OR C2H4 + Br2 -> C2H4Br2
• React with hydrogen bromide OR C2H4 + HBr ->
C2H5Br
•React with steam OR heat with water OR C2H4 + H2O(g) -> C2H5OH
• Acid (catalyst)
• Electrophilic addition

Question 4

What does a curly arrow represent

Answer 4

• Movement of electron pair

Question 5

Ethan-1,2-diol is much less volatile than ethanol

Answer 5

• Ethane-1,2-diol has more OH groups (than ethanol)
• Stronger hydrogen bonding (between ethane-1,2-diol
molecules)

Question 6

State 2 modern analytic techniques that scientists can use to monitor environmental pollution

Answer 6

• IR (spectroscopy)
• Mass spectrometry
• UV (spectroscopy)

Question 7

Explain why it is important to establish international cooperation to reduce pollution levels

Answer 7

• All countries contribute towards pollution

* Allows monitoring of pollution in different countries

Question 8

Complete the equations below that describe how NO contributes to ozone depletion

Answer 8

• NO + O3 -> NO2 + O2
• NO2 + O -> NO + O2
• O3 + O -> 2O2

Question 9

It is not possible to measure the enthalpy change of formation of N2O(g)

Suggest why

Answer 9

• Reaction gives NO/NO2
• Activation energy too high
• Rate of reaction is too slow

Question 10

Explain how atmospheric methane molecules can contribute to global warming

Answer 10

• Absorbs IR radiation

* Bonds vibrate

Question 11

State and explain the difference in rates of hydrolysis of 1-bromopentane and 1-chloropentane

Answer 11

• 1-bromopentane reacts faster OR 1-chloropentane reacts slower
• Bond enthalpy of C–Cl greater (than C–Br bond)
• C–Cl stronger bond (than C–Br bond)

Question 12

Exlpain the shape of ethene molecule. State the H-C-H bond angle in ethene

Answer 12

• 120

* Three areas of electron density repel each other

Question 13

The pressure of the mixture is increased. Explain what happens to the position of equilibrium

CH4 + H20 -> CO + 3H2 ∆H = +210

Answer 13

• (Equilibrium position shifts) to the left
• (Because there are) fewer moles (of gas) on the reactant
side
•

Question 14

The temperature of the equilibrium mixture is increased . Explain what happens to the position of the equilibrium

CH4 + H20 -> CO + 3H2 ∆H = +210

Answer 14

• (Equilibrium position shifts) to the right

* (Because forward) reaction is endothermic

Question 15

Suggest why the manufactures used a pressure of 30 atm CH4 + H20 -> CO + 3H2 ∆H = +210

Answer 15

• Gives a high rate of reaction

Question 16

Nickel catatlyst increases rate. Explain using a Boltzmann diagram

Answer 16

• y-axis label is (number of) molecules’ AND x-axis
label is ‘energy
• Lowers activation energy
• More molecules with energy above activation energy with a catalyst

Question 17

Suggest two reasons why it is important to use carbon monoxide to make methanol

Answer 17

• Carbon monoxide is toxic

* Methanol is a fuel

Question 18

Give two reasons why many organic proudcts of the reaction between bromine and ethane

Answer 18

• Multi-substitution can occur
• More than one C–H bond can be substituted
• Lots of termination steps
• Termination steps can give products that will also react with (bromine) radicals