10.2.1 Application of Alcohols as Fuels

Methanol:

• Methanol has been used as an alternative fuel for cars.
• However, it has a low energy content as compared to gasoline, diesel, or ethanol.
• So, methanol reduces the driving range of the vehicles.

Ethanol:

• Ethanol, on the other hand, is a more useful fuel.
• It produces about two-thirds as much energy per litre as gasoline.
• Ethanol has a higher octane number than gasoline.
• Petrol blended with 10-20% ethanol is used in many countries, for example Brazil.
• This mixture is commonly known as gasohol.

Advantages of ethanol as a fuel:

• Ethanol increases the octane value of fuel.
• It cuts down the formation of carbon monoxide and other smog-causing emissions.
• Ethanol is a renewable energy source, whereas fossil fuels are non-renewable.
• Pollution is a major disadvantage of fossil fuels.

Recent studies (from the source):

- According to recent studies conducted at Harvard, USA, corn-based ethanol reduces greenhouse gas emissions by roughly 40-50%.

Disadvantage of using alcohols as fuel:

• Alcohols can corrode certain materials used in engines.
• This is due to their hygroscopic nature (they absorb significant amounts of water from air) compared to gasoline.

Key point: Ethanol is a more useful fuel than methanol. It has a higher octane number, reduces harmful emissions, and is renewable. However, alcohols can corrode engine materials.

Summary Table

Intermediate Level

Combustion of alcohols:

• Alcohols are flammable.
• They burn in oxygen to produce CO₂, H₂O, and heat.
• General equation: Alcohol + O₂ → CO₂ + H₂O + heat

Applications:

Methanol:

• Alternative fuel for cars.
• Low energy content compared to gasoline, diesel, or ethanol.
• Reduces driving range.

Ethanol:

• More useful fuel.
• Produces about two-thirds as much energy per litre as gasoline.
• Higher octane number than gasoline.
• Petrol blended with 10-20% ethanol is called gasohol.
• Used in countries like Brazil.
• Increases octane value.
• Cuts down carbon monoxide and smog-causing emissions.
• Renewable energy source.

Disadvantage:

• Alcohols can corrode certain materials used in engines.
• They are hygroscopic (absorb water from air).

Key point: Ethanol is a more useful fuel than methanol. It has a higher octane number and is renewable, but it can corrode engine materials.

Solved Example

Example: Write the Equation for the Combustion of Ethanol

Question: Write the balanced chemical equation for the complete combustion of ethanol.

Solution:

Reactants: Ethanol (CH₃CH₂OH) and oxygen (O₂)

Products: Carbon dioxide (CO₂) and water (H₂O)

Equation:

CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat

Final Answer: CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat

Example: Write the Equation for the Combustion of Methanol

Question: Write the balanced chemical equation for the complete combustion of methanol.

Solution:

Reactants: Methanol (CH₃OH) and oxygen (O₂)

Products: Carbon dioxide (CO₂) and water (H₂O)

Equation:

CH₃OH + 2O₂ → CO₂ + 2H₂O + heat

Final Answer: CH₃OH + 2O₂ → CO₂ + 2H₂O + heat

Important Points

• - Alcohols are flammable organic compounds.
• - They burn in the presence of oxygen to form carbon dioxide, water, and release energy.
• - This makes it possible to use alcohol as a fuel.
• - Methanol:
• - Alternative fuel for cars.
• - Low energy content.
• - Reduces driving range.
• - Ethanol:
• - More useful fuel.
• - Produces about two-thirds as much energy per litre as gasoline.
• - Higher octane number than gasoline.
• - Petrol blended with 10-20% ethanol is called gasohol.
• - Used in countries like Brazil.
• - Increases octane value.
• - Cuts down carbon monoxide and smog-causing emissions.
• - Renewable energy source.
• - Disadvantage: Alcohols can corrode certain materials used in engines (hygroscopic nature).
• - Recent studies: Corn-based ethanol reduces greenhouse gas emissions by roughly 40-50%.
• - Equations:
• - Methanol: CH₃OH + 2O₂ → CO₂ + 2H₂O + heat
• - Ethanol: CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat

Remember

• - Alcohols are flammable.
• - They burn in oxygen to produce CO₂, H₂O, and heat.
• - Methanol: alternative fuel; low energy content.
• - Ethanol: more useful fuel; higher octane number; renewable.
• - Gasohol = petrol blended with 10-20% ethanol.
• - Ethanol reduces CO and smog-causing emissions.
• - Alcohols can corrode engine materials (hygroscopic).
• - Corn-based ethanol reduces greenhouse gas emissions by 40-50%.
• - Equations:
• - Methanol: CH₃OH + 2O₂ → CO₂ + 2H₂O + heat
• - Ethanol: CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat

Common Mistakes

Quick Revision

Combustion of Alcohols:

Alcohols are flammable organic compounds. They burn in the air due to the presence of a hydrocarbon chain. Just like fossil fuels, all alcohols burn in the presence of oxygen to form carbon dioxide water and release energy. This feature makes it possible to use alcohol as a fuel. In countries where there is no oil industry, ethanol produced by fermentation is used as an alternative fuel to imported oil.

• CH₃OH + 2O₂ → CO₂ + 2H₂O + heat

• CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat

10.2.1 Application of Alcohols as Fuels:

Methanol has been used as an alternative fuel for cars. However, it has a low energy content as compared to gasoline, diesel, or ethanol. So, methanol reduces the driving range of the vehicles. Ethanol, on the other hand, is a more useful fuel. It produces about two-thirds as much energy per litre as gasoline. Ethanol has a higher octane number than gasoline. Petrol blended with 10-20% ethanol is used in many countries, for example Brazil. This mixture is commonly known as gasoline. Ethanol not only increases the octane value of fuel but also cuts down the formation of carbon monoxide and other smog-causing emissions. Moreover, ethanol is a renewable energy source. Whereas, fossil fuels are non-renewable energy source. At the same time, pollution is a major disadvantage of fossil fuels.

According to recent studies conducted at Harward, USA, corn-based ethanol reduces greenhouse gas emissions by roughly 40-50%.

The disadvantage of using alcohols as fuel is that it can corrode certain materials used in engines. This is due to their much hygroscopic nature than gasoline, so, they absorb significant amounts of water from air.

60-Second Revision

• Alcohols are flammable.
• They burn in oxygen to produce CO₂, H₂O, and heat.
• Methanol: alternative fuel; low energy content.
• Ethanol: more useful fuel; higher octane number; renewable.
• Gasohol = petrol blended with 10-20% ethanol.
• Ethanol reduces CO and smog-causing emissions.
• Alcohols can corrode engine materials (hygroscopic).
• Corn-based ethanol reduces greenhouse gas emissions by 40-50%.
• Equations:
• Methanol: CH₃OH + 2O₂ → CO₂ + 2H₂O + heat
• Ethanol: CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O + heat
• ⚠️ Warning: alcohols can corrode engine materials due to their hygroscopic nature — they absorb water from the air.