Energy from Fuels (DP IB Chemistry)

Incomplete combustion is the burning of a fuel in limited supplies of oxygen resulting in the formation of carbon monoxide and/or carbon and water.

The balanced symbol equation for the incomplete combustion of methanol is:

CH₃OH + O₂ → CO + 2H₂O

The balanced symbol equation for the incomplete combustion of butane is:

2C₄H₁₀ (g) + 9O₂ (g) → 8CO (g) + 10H₂O (g)

False.

Incomplete combustion will always form water instead of hydrogen.

True.

Incomplete combustion is an example of an exothermic reaction.

Three fossil fuels are:

• Coal

• Natural gas

• Crude oil

False.

As the length of the hydrocarbon chain increases, it releases less energy per unit mass of fuel.

As the length of the hydrocarbon chain increases, more carbon dioxide is produced per gram of hydrocarbon burnt.

True.

Natural gas is hard to store.

Methane releases the most energy per unit mass when combusted.

Advantages of using coal as a fuel include:

• It is relatively cheap,

• It is abundant,

• It has a long lifespan compared to other fossil fuels.

Disadvantages of using coal as a fuel include:

• It produces carbon dioxide which causes global warming,

• It produces sulfur dioxide which causes acid rain,

• It produces particulates which cause global dimming,

• Mining of coal causes destruction of habitats and noise pollution.

True.

Fossil fuels contain hydrocarbons.

A non-renewable resource is a resource that is of finite supply, which means that it cannot be replenished quickly.

False.

A disadvantage of using oil as a fuel is that it releases sulfur dioxide which causes acid rain.

Greenhouse gases include:

• carbon dioxide

• water vapour

• methane

• nitrous oxides

The greenhouse effect refers to greenhouse gases in the atmosphere absorbing and trapping radiation emitted from the Earth's surface, causing warming.

The environmental effect of the increased amount of greenhouse gases in the atmosphere is climate change / global warming.

The type of radiation from the sun which gets absorbed and re-emitted as infrared by the Earth's surface is long wavelength radiation / UV.

False.

Some thermal energy from the Sun is re-emitted from the Earth's surface.

The greenhouse effect in terms of short and long wavelength radiation is:

• Short wavelength radiation (ultraviolet radiation) is emitted from the sun

• Some of it is absorbed by the Earth's surface and some is re-emitted as long wavelength radiation (infrared radiation)

• Much of the radiation is trapped inside the Earth’s atmosphere by greenhouse gases

Two human activities which are contributing to the release of methane are landfill sites and farming.

Two activities which release carbon dioxide into the atmosphere are the combustion of fossil fuels and deforestation.

True.

Increasing amounts of greenhouse gases in the atmosphere cause average global temperatures to increase.

A biofuel is a fuel produced from the biological fixation of carbon over a short period of time through photosynthesis.

A renewable resource is one which will not run out in the foreseeable future because they can be replaced over a short period of time.

The three main types of biofuel are:

• Bioethanol,

• Biodiesel,

• Biogas.

False.

Biofuels are an example of a renewable resource.

Advantages of using biofuels include:

• They are carbon neutral,

• They reduce the amount of waste going to landfill,

• They reduce greenhouse gas emissions.

Disadvantages of using biofuels include:

• They are expensive,

• They have a lower specific energy than fossil fuels,

• They remove nutrients from the ground,

• They use large amounts of pesticide and fertilisers.

The process used to produce bioethanol is fermentation.

Biofuels are considered carbon neutral because the carbon dioxide they absorb during the photosynthesis is equal to the amount produced by the combustion of the biofuel.

There is no overall loss or gain in carbon dioxide in the atmosphere.

The main component of biogas is methane.

The process used to produce biogas is transesterification.

An advantage of using biofuels over fossil fuels is that they are renewable and can be carbon neutral if crops are replanted.

A disadvantage of large-scale biofuel production is that it can lead to deforestation and compete with food production for land use.

A fuel cell is used to convert chemical energy from a fuel directly to electrical energy.

A fuel cell works by the fuel donating electrons at one electrode, and oxygen gaining electrons at the other electrode.

The reactants in a hydrogen-oxygen fuel cell are hydrogen and oxygen.

False.

Fuel cells do not store energy like batteries.

The product of a hydrogen-oxygen fuel cell is ‎water.

An advantage of fuel cells over internal combustion engines is that they produce only water as a byproduct, making them more environmentally friendly.

Advantages of methanol fuel cells over hydrogen fuel cells include:

• Methanol is easier to store and transport than hydrogen,

• Methanol can be produced from renewable resources,

• Methanol produces more energy than hydrogen.

Disadvantages of using hydrogen in fuel cells include:

• Hydrogen is highly flammable and difficult to store safely,

• Hydrogen is produced from finite resources,

• Expensive equipment is needed to store hydrogen.

The half equation for the reaction that occurs at the anode in a hydrogen-oxygen fuel cell is:

2H₂ (g) + 4OH^– (aq)  →  4H₂O (l) +  4e^–              

The overall equation for the reaction that occurs in a methanol fuel cell is:

CH₃OH (aq) + 1.5O₂ (g) → CO₂ (g) +2H₂O (l) 

OR

2CH₃OH (aq) + 3O₂ (g) → 2CO₂ (g) +4H₂O (l)

True.

The half equation for the reaction at the cathode ins a methanol fuel cell is:

O₂ (g) + 4H⁺ (aq) + 4e^– →  2H₂O (l)