2012 Chains, Energy Resources

Question 1

Explain why petroleum industry processes straight chains into cyclic hydrocarbons

Answer 1

• Cyclic hydrocarbons have more efficient combustion

Question 2

What is meant by the term stereoisomers

Answer 2

• Same structural formula

* Different arrangement (of atoms) in space

Question 3

What is meant by the functional group

Answer 3

• Group of atoms (in a molecule or compound) that is
responsible for the reactions
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Question 4

What is meant by the radical

Answer 4

• Species with an unpaired electron

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Question 5

What is meant by standard enthalpy change of formation

Answer 5

• (Enthalpy change) when one mole of a compound
• Is formed from its elements
• Under standard conditions

Question 6

H2 + Cl2 -> 2HCl ∆H = -184

The pressure is increased. What happens to the rate of of the reaction

Answer 6

• More concentration of particles

* More frequent collisions

Question 7

The temperature decreases. Explain the effect using Boltzmann diagram

Answer 7

• y-axis label is ‘(number of) molecules’ AND x-axis label is ‘energy’
• Activation energy does not change
• Fewer molecules have energy above activation energy OR fewer molecules have enough energy to react
• So fewer successful collisions

Question 8

Suggest why CF2Cl2 does not hydrolyse in water

Answer 8

• C–F or C–Cl ) bonds need a large amount of energy to break 
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Question 9

Exlpain how the presence of CFCs in the upper atmosphere leads to ozone depletion

Answer 9

• CF2Cl2 -> CF2Cl + Cl
• Cl catalyses the decomposition of ozone
• Cl + O3 -> ClO + O2
• ClO + O -> Cl + O2

Question 10

Use of CFCs has decreased. Suggest why

Answer 10

• Because (more) UV will reach the Earth’s surface and risk of (skin) cancer increased
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