Photo AI

Ethane reacts with chlorine to form chloroethane - CIE - A-Level Chemistry - Question 3 - 2015 - Paper 1

Question 3

Ethane reacts with chlorine to form chloroethane. C2H6(g) + Cl2(g) → C2H5Cl(g) + HCl(g) a) Use bond energies from the Data Booklet to calculate the enthalpy change... show full transcript

Worked Solution & Example Answer:Ethane reacts with chlorine to form chloroethane - CIE - A-Level Chemistry - Question 3 - 2015 - Paper 1

Step 1

Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction. Include a sign in your answer.

96%

114 rated

Answer

To calculate the enthalpy change for the reaction, we need to consider the bond energies involved:

Bond Breaking:
- Bond breaking involves the following bonds:
  - C–H bonds in ethane (C2H6): 6 bonds at 410 kJ each.
  - Cl–Cl bond: 1 bond at 242 kJ.
- Total energy for bond breaking is:
  
  $ext{Energy for breaking} = (6 imes 410) + 242 = 2460 + 242 = 2702 ext{ kJ}$
Bond Forming:
- Forming bonds involves:
  - C–Cl bond in chloroethane (C2H5Cl): 1 bond at 340 kJ.
  - H–Cl bond: 1 bond at 431 kJ.
- Total energy for bond forming is:
  
  $ext{Energy for forming} = 340 + 431 = 771 ext{ kJ}$
**Enthalpy Change:
$ext{Enthalpy change} = ext{Total energy to break bonds} - ext{Total energy to form bonds}$ $= 2702 - 771 = 1931 ext{ kJ}$
- Therefore, the enthalpy change for the reaction is +1931 kJ mol⁻¹.

Step 2

State the conditions needed for this reaction to occur.

99%

104 rated

Answer

The reaction between ethane and chlorine requires specific conditions, which are:

UV light or high temperature / sunlight to initiate the reaction.

Step 3

Use a series of equations to describe the mechanism of this reaction including the names of each stage and an indication of how butane can be produced as a minor by-product.

96%

101 rated

Answer

The reaction mechanism can be divided into three stages:

Initiation:
- Chlorine molecules (Cl2) dissociate into two chlorine radicals (Cl·):

ightarrow 2 ext{Cl}^{ullet}$$

Propagation:
- A chlorine radical abstracts a hydrogen atom from ethane, forming chloroethane and a second chlorine radical:

ightarrow ext{C}_2 ext{H}_5 ext{Cl} + ext{H}^{ullet}$$

The newly formed radical can react with another chlorine molecule to regenerate chlorine radicals:

ightarrow ext{C}_2 ext{H}_5 ext{Cl} + ext{Cl}^{ullet}$$

Minor by-product: Butane can be produced if the hydrogen atom abstracted comes from another ethyl radical:

ightarrow ext{C}4 ext{H}{10}$$

Termination:
- All radicals combine to end the chain reaction, e.g.,

ightarrow ext{Cl}_2 ext{C}_2 ext{H}_5^{ullet} + ext{H}^{ullet} ightarrow ext{C}_2 ext{H}_6$$.

Step 4

Give the name of X.

98%

120 rated

Answer

The name of the intermediate compound X is ethene.

Step 5

Suggest the reagent and conditions needed for reaction 1.

97%

117 rated

Answer

The reagent for reaction 1 is KOH or NaOH, and the conditions required are ethanol as the solvent and heat under reflux.

Step 6

Suggest the reagent and conditions needed for reaction 2.

97%

121 rated

Answer

For reaction 2, the reagent is H2 along with a catalyst such as Pt (platinum) or Ni (nickel).

Ethane reacts with chlorine to form chloroethane - CIE - A-Level Chemistry - Question 3 - 2015 - Paper 1

Worked Solution & Example Answer:Ethane reacts with chlorine to form chloroethane - CIE - A-Level Chemistry - Question 3 - 2015 - Paper 1

Use bond energies from the Data Booklet to calculate the enthalpy change for this reaction. Include a sign in your answer.

State the conditions needed for this reaction to occur.

Use a series of equations to describe the mechanism of this reaction including the names of each stage and an indication of how butane can be produced as a minor by-product.

Give the name of X.

Suggest the reagent and conditions needed for reaction 1.

Suggest the reagent and conditions needed for reaction 2.

Join the A-Level students using SimpleStudy...

Other A-Level Chemistry topics to explore