Combustion & Fuel Cells

Combustion

Combustion occurs when a substance burns in oxygen to release energy.

All metals can combust

False. Not all metals can combust. Some metals will only combust if they have a high surface area.

Product formed when a metal undergoes combustion

When a metal undergoes combustion a metal oxide is formed.

General word equation for the combustion of non-metals

The general word equation for the combustion of non-metals is: Non-metal + oxygen → non-metal oxide.

Complete combustion

Complete combustion is when a fuel burns in a plentiful supply of oxygen to form carbon dioxide and water.

Balanced symbol equation for the complete combustion of methane

The balanced symbol equation for the complete combustion of methane is: CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (l).

Balanced symbol equation for the complete combustion of ethanol

The balanced symbol equation for the complete combustion of ethanol is: C2H5OH (g) + 3O2 (g) → 2CO2 (g) + 3H2O (l).

Metals react with oxygen

True. When metals react with oxygen, they form basic metal oxides.

Oxide formed when non-metals undergo combustion

When non-metals undergo combustion they form acidic oxides.

Balanced symbol equation for the combustion of potassium

The balanced symbol equation for the combustion of potassium is: 4K + O2 → 2K2O.

Incomplete combustion

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.

Balanced symbol equation for the incomplete combustion of methanol

The balanced symbol equation for the incomplete combustion of methanol is: CH3OH + O2 → CO + 2H2O.

Balanced symbol equation for the incomplete combustion of butane

The balanced symbol equation for the incomplete combustion of butane is: 2C4H10 (g) + 9O2 (g) → 8CO (g) + 10H2O (g).

Incomplete combustion can produce hydrogen

False. Incomplete combustion will always form water instead of hydrogen.

Incomplete combustion is an exothermic reaction

True. Incomplete combustion is an example of an exothermic reaction.

Three fossil fuels

Three fossil fuels are: Coal, Natural gas, Crude oil.

Length of hydrocarbon chain and energy release

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

Carbon dioxide produced and hydrocarbon chain length

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

Natural gas storage

True. Natural gas is hard to store.

Alkane that releases the most energy per unit mass

Methane releases the most energy per unit mass when combusted.

Advantages of using coal as a fuel

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

It produces carbon dioxide which causes global warming, sulfur dioxide which causes acid rain, particulates which cause global dimming, and mining of coal causes destruction of habitats and noise pollution.

Fossil fuels

Fossil fuels contain hydrocarbons.

Non-renewable resource

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

Disadvantage of using oil

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

Greenhouse gases

Greenhouse gases include carbon dioxide, water vapour, methane, and nitrous oxides.

Greenhouse effect

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

Environmental effect of greenhouse gases

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

Radiation absorbed by Earth's surface

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.

Thermal energy absorption

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

Greenhouse effect in terms of radiation

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.

Human activities releasing methane

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

Human activities releasing carbon dioxide

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

Greenhouse gases and global temperatures

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

Biofuel

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

Renewable resource

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.

Types of biofuel

The three main types of biofuel are Bioethanol, Biodiesel, and Biogas.

Biofuels as a resource

Biofuels are an example of a renewable resource.

Advantages of using biofuels

Give two advantages of using biofuels.

Advantages of using biofuels

They are carbon neutral, they reduce the amount of waste going to landfill, they reduce greenhouse gas emissions.

Disadvantages of using biofuels

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.

Process used to produce bioethanol

Fermentation.

Why are biofuels considered carbon neutral?

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

Main component of biogas

Methane.

Process used to produce biogas

Transesterification.

Advantage of using biofuels over fossil fuels

They are renewable and can be carbon neutral if crops are replanted.

Disadvantage of large-scale biofuel production

It can lead to deforestation and compete with food production for land use.

What is a fuel cell?

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

How does a fuel cell work?

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

Reactants in a hydrogen-oxygen fuel cell

Hydrogen and oxygen.

Fuel cells store energy like batteries

False. Fuel cells do not store energy like batteries.

Product of a hydrogen-oxygen fuel cell

Water.

Advantage of fuel cells over internal combustion engines

They produce only water as a byproduct, making them more environmentally friendly.

Advantage of methanol fuel cells over hydrogen fuel cells

Methanol is easier to store and transport than hydrogen, methanol can be produced from renewable resources, methanol produces more energy than hydrogen.

Disadvantage of using hydrogen in fuel cells

Hydrogen is highly flammable and difficult to store safely, hydrogen is produced from finite resources, expensive equipment is needed to store hydrogen.

Half-equation for the reaction at the anode in a hydrogen-oxygen fuel cell

2H2 (g) + 4OH- (aq) → 4H2O (l) + 4e-.

Overall equation for the reaction in a methanol fuel cell

CH3OH (aq) + 1.5O2 (g) → CO2 (g) + 2H2O (l) OR 2CH3OH (aq) + 3O2 (g) → 2CO2 (g) + 4H2O (l).

Half equation for the reaction at the cathode in a methanol fuel cell

O2 (g) + 4H+ (aq) + 4e- → 2H2O (l).