Fuels (Edexcel GCSE Combined Science: Chemistry): Flashcards

True.

The size and length of each hydrocarbon molecule determines which fraction it will be separated into.

Viscosity is the ease of flow of a liquid.

As the number of carbon atoms increases, the viscosity of the liquid increases.

False.

As you move up a fractionating column, the temperature decreases.

As the molecular size increases, the boiling point of a hydrocarbon increases.

Diesel is used in diesel engines (gas oil).

Liquefied petroleum gas is used for domestic heating and cooking.

Heavy fuel oil is used for ships and power stations.

The fraction used for surfacing roads is bitumen.

True.

Kerosene is used as jet fuel (paraffin).

Fractions condense inside the fractionation tower because their vapours rise and reach a point where the temperature is below their boiling point.

As the molecules get larger, the intermolecular forces of attraction between the molecules become greater, so more energy is needed to overcome them.

In fractional distillation, crude oil is heated and the vapours rise up the fractionating column. Fractions with lower boiling points condense near the top of the column.

A homologous series is a family or group of organic compounds that have similar features and chemical properties due to having the same functional group.

All members of a homologous series have:

• The same general formula

• The difference in molecular formula between one member and the next is CH₂

• Gradation in their physical properties

• The same functional group

• Similar chemical properties

Members of the same homologous series share the same functional group, have the same general formula, and differ from one another by a CH₂ unit.

A functional group is a specific group of atoms within a molecule that determines the chemical properties of that molecule.

As the molecules get larger in a homologous series, the boiling points gradually increase due to greater intermolecular forces of attraction.

False.

Compounds in the same homologous series have similar chemical properties.

The products of complete combustion of hydrocarbons are carbon dioxide and water.

Incomplete combustion occurs when there is insufficient oxygen to burn the fuel completely.

The products of incomplete combustion are carbon monoxide, carbon (soot) and water.

Carbon monoxide binds well to haemoglobin, preventing it from binding to oxygen and transporting oxygen to organs.

False.

Carbon dioxide is a pollutant causing global warming and climate change.

Incomplete combustion occurs in some appliances such as:

• Boilers

• Stoves

• Internal combustion engines

The symbol equation for the complete combustion of propane is:

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

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

C₂H₆ + 2.5O₂ → 2CO + 3H₂O

Four gases that the burning of fossil fuels releases:

• Carbon dioxide

• Carbon monoxide

• Oxides of nitrogen

• Oxides of sulfur

A fuel is a substance that is burned to release thermal energy.

A common impurity in fuels that contributes to acid rain is sulfur.

When burned, sulfur reacts with oxygen to form sulfur dioxide (SO₂), which dissolves in rainwater to form acid rain.

Complete combustion of a hydrocarbon in excess oxygen produces carbon dioxide and water only, whereas incomplete combustion can produce carbon monoxide and soot (carbon).

Nitrogen oxides are formed in the high pressure and temperature conditions of internal combustion engines and blast furnaces.

The equation for the oxidation of sulfur is:

S (s) + O₂ (g) → SO₂ (g)

Acid rain is formed when nitrogen and sulfur oxides dissolve in rainwater to form nitric acid and sulfuric acid, respectively.

Harmful effects of sulfur dioxide include:

• Acid rain

• Corrosion of buildings and structures

• Damage to aquatic organisms

• Damage to plant life

• Respiratory problems

Catalytic converters reduce harmful pollutant gases in vehicle exhaust, converting carbon monoxide and nitrogen oxides into less harmful gases.

Two gases that contribute to acid rain are nitrogen dioxide and sulfur dioxide.

During combustion, the sulfur impurities in the fossil fuels get oxidised / react with oxygen to form sulfur dioxide.

The equation to show the formation of acid rain, H₂SO₄ (aq), from sulfur dioxide, water and oxygen is:

2SO₂ (g) + O₂ (g) + 2H₂O (l) → 2H₂SO₄ (aq)

True.

At the high temperatures inside a combustion engine, nitrogen and oxygen from the air react to form nitrogen oxides, which contribute to acid rain and photochemical smog.

Acid rain is rain with a lower pH than normal, caused by sulfur dioxide and nitrogen oxides dissolving in rainwater to form sulfuric acid and nitric acid respectively.

Sulfur dioxide is produced during the combustion of fossil fuels because they contain sulfur impurities, which react with oxygen to form SO₂ gas.

The type of fuel that provides most of the world's energy is fossil fuels.

A fuel is a substance which when burned, releases thermal energy.

The symbol equation for the reaction of hydrogen with oxygen is:

2H₂ + O₂ → 2H₂O

Advantages of using hydrogen as a fuel are:

• It releases more energy per kilogram than any other fuel (except for nuclear fuels)

• It does not pollute as it only produces water on combustion, no other product is formed

The disadvantages of using hydrogen as a fuel are:

• Expensive to produce and requires energy for the production process

• Difficult and dangerous to store and move around (usually stored as liquid hydrogen in highly pressurised containers)

• The production of hydrogen process releases carbon dioxide 

The type of reaction which occurs when hydrogen and oxygen react to form water is exothermic or combustion.

Fossil fuels include:

• Coal

• Oil

• Natural gas

The main compound in natural gas is methane, CH₄.

False.

Burning hydrogen produces only water (H₂O), making it a clean fuel with no carbon dioxide emissions at the point of use.

Hydrogen is considered a clean fuel because its only combustion product is water, but a disadvantage is that it is difficult and dangerous to store and transport.

Cracking is a thermal decomposition reaction in which long-chain hydrocarbon molecules are broken down into shorter, more useful alkane and alkene molecules using heat and a catalyst.

True.

The demand for certain fractions outstrips the supply, which is why cracking is necessary to convert surplus unwanted fractions into more useful ones.

The purpose of cracking is to convert surplus unwanted fractions of crude oil, such as kerosene and diesel oil, into more useful fractions like petrol (gasoline), alkenes and hydrogen.

Cracking converts long-chain hydrocarbons into shorter, more useful molecules including alkanes (used as fuel) and alkenes (used to make polymers).

The two methods used for cracking alkanes are:

• Catalytic cracking

• Steam cracking

False.

Cracking is an endothermic reaction.

The equation for the cracking of decane to produce octane and ethene is:

C₁₀H₂₂ → C₈H₁₈ + C₂H₄

True.

Alkanes are saturated compounds, and alkenes are unsaturated compounds.

The catalyst used in catalytic cracking is aluminium oxide (alumina / Al₂O₃).

False.

Cracking is a type of thermal decomposition reaction.

A long chain hydrocarbon is cracked to form short chain alkanes and short chain alkenes.

Examples of longer chain fractions of crude oil are:

• Fuel oil

• Bitumen

True.

Long chain fractions are in high supply but in low demand.

This explains why they are cracked into more useful, shorter chain alkanes and alkenes.

Short-chain alkenes from cracking can be used to make polymers / plastics.