2014 Chains, Energy and Resources

Question 1

What is meant by the term homologous series

Answer 1

• Series of compounds with the same functional group but with each successive member differing by CH2

Question 2

State the general formula cycloalkanes

Answer 2

• CnH2n

Question 3

Cyclopropane -33
Cyclopentane 49
Cyclohexane 81

Explain the increase in boiling points of the cycloalkanes shown above

Answer 3

• More carbons (in ring)/more areas of surface contact
• Stronger London forces
• More energy needed to break the intermolecular forces

Question 4

The C-C- bond angles in cyclohexane are 109.5

State and explain the shape around each carbon atom in cyclohexane

Answer 4

• Tetrahedral

* Four bonding pairs repel/four bonds repel

Question 5

Explain what is meant by the term stereosiomers

Answer 5

• Compounds with the same structural formula but a different arrangement of atoms in space

Question 6

Explain why the initiation step is an example of homolytic fission

Answer 6

• The breaking of a (Br-Br) bond
• Forms two radicals
• The breaking of a (Br-Br) bond one
• One electron (from the bond pair) goes to each atom/bromine

Question 7

A closed system is required for dynamic equilibrium to be established

State one other feature of this dynamic equilibrium

Answer 7

• Rate of the forward reaction is equal to the rare of the reverse reaction
• Concentration do not change

Question 8

The student heats the equilibrium mixture keeping the volume constant
Predict how the composition of the equilibrium mixture changes on heating

H2 + I2 -> 2HI ∆H =-9

Answer 8

• More H2 and I2 OR less HI 
• Equilibrium position shifts to the left
• Forward reaction is exothermic/reverse reaction is endothermic

Question 9

Predict and explain what effect, if any, an increase in the pressure would have on the position of the equilibrium

H2 + I2 -> 2HI ∆H =-9

Answer 9

• No effect

* Same number of (gaseous) moles on both sides

Question 10

What is meant by the term standard enthalpy change of formation

Answer 10

• Enthalpy change when one mole of a compound
• Is formed from its elements
• Under Standard conditions
- 298K
- 100 kPa/101kPa

Question 11

The greenhouse effect of carbon dioxide in the atmosphere is dependent on two factors

Answer 11

• Amount (in atmosphere)
• Ability to absorb infrared/IR radiation
• Residence time

Question 12

Explain how sodium hydrogencarbonate removes hydrogen chloride

Answer 12

• Sodium hydrogencarbonate neutralises HCl

Question 13

Describe and explain the effect of decreasing the pressure on the rate of a reaction

Answer 13

• Decreasing the pressure decreases the rate of reaction
• Decreased concentration of molecules
• Less frequent collisions

Question 14

Structural isomers

Answer 14

• Compounds having the same molecular formula but different structural formulae

Question 15

Describe the oxidation reactions of propan-1-ol when using a suitable oxidising agent.

Answer 15

Reagents
• Acid/H+ and (potassium or sodium) dichromate/Cr2O72-
Observations 
• Orange to Green
• Distillation produces aldehyde 
• Reflux produces carboxylic acid

Question 16

Suggest one advantage of adding cyclohexane to hexane in petrol

Answer 16

• Cyclohexane will burn more efficiently

Question 17

Explain how the use of 1-iodobutane would affect the rate of reaction compared with 1-bromobutane

Answer 17

• 1-Iodobutane increases the rate

* C—I bonds are weaker (than C—Br)

Question 18

Explain how increasing the temperature increases the rate of reaction
Include Boltzmann sketch

Answer 18

• Axes labelled (number of) molecules on y-axis and (kinetic) energy on x-axis
• At a higher temperature) more molecules have energy
above activation energy OR greater area under the curve above the activation energy
•