This question is about alkenes and alcohols - AQA - GCSE Chemistry - Question 10 - 2021 - Paper 2

The conditions used to produce ethene from large hydrocarbon molecules typically involve high temperature, usually in the range of 300 to 900 °C, and the presence of steam and possibly a catalyst.

To produce ethanol economically from the reaction of ethene and steam, the following conditions should be considered:

1. High Temperature: A higher temperature increases the reaction rate but can decrease yield due to the exothermic nature of the reaction. It is essential to find a compromise that promotes the reaction rate without significantly reducing the yield.

2. Pressure: Higher pressure can shift the equilibrium to favor product formation, which is beneficial for the yield of ethanol. However, it also increases costs associated with stronger reaction vessels.

3. Catalyst: Using a catalyst can enhance the reaction rate at lower temperatures, thus maintaining a good yield while reducing the energy costs.

4. Equilibrium Consideration: The reaction is reversible, so conditions should favor the forward reaction, ensuring that excess reactants are present to shift the equilibrium towards the formation of ethanol.

The process of producing ethanol from sugar solution by adding yeast is called fermentation.

To produce butanol from sugar solution by adding bacteria, the following conditions are recommended:

1. Warm Temperature: A temperature in the range of 25 °C to 45 °C should be maintained for optimal bacterial activity.

2. Anaerobic Conditions: The reaction must take place in the absence of oxygen.

To calculate the number of moles of ethanol needed to travel 200 km:

1. Convert distance:

   200 ext{ km} = 200000 ext{ m}

2. Calculate energy required:

   ext{Energy} = 1.95 ext{ kJ/m} imes 200000 ext{ m} = 390000 ext{ kJ}

3. Moles of ethanol:

   ext{Moles} = rac{ ext{Total energy needed}}{ ext{Energy per mole}} = rac{390000 ext{ kJ}}{1300 ext{ kJ/mol}} = 300 ext{ moles}.

The balanced equation for the complete combustion of butanol (C₄H₁₀O) is:

C₄H₁₀O + 6 O₂ → 4 CO₂ + 5 H₂O