Crude Oil, Fuels & Organic Chemistry (WJEC GCSE Science (Double Award): Chemistry): Flashcards

Bitumen is the crude oil fraction used to surface roads and roofs. It is the heaviest fraction with the highest boiling point.

Petroleum gases are used as fuel for domestic heating and cooking (e.g. in gas stoves and boilers).

True.

Viscosity increases with chain length because longer molecules have stronger intermolecular forces, making the liquid thicker and harder to flow.

Viscosity is a measure of how easily a liquid flows. Liquids with high viscosity are thick and flow slowly; those with low viscosity are runny.

Flammability decreases as chain length increases because smaller hydrocarbon molecules are more easily ignited than larger ones.

Longer chain hydrocarbons burn with a more yellow smoky flame, while shorter chain hydrocarbons burn with a cleaner blue flame.

False.

Kerosene is used as jet fuel. Diesel is used as fuel for cars and some trains.

Longer chain alkanes are useful as lubricants because their high viscosity means they are less likely to burn and they reduce friction between moving parts in machinery.

Two environmental impacts of burning crude oil are:

1. Releasing carbon dioxide, a greenhouse gas that contributes to global warming

2. Releasing sulfur dioxide (from sulfur impurities), which causes acid rain

False.

Oil spillages can have a devastating effect on the local environment, killing animals and destroying habitats far beyond national borders.

Burning crude oil releases carbon dioxide, which contributes to global warming and climate change.

Acid rain is rain made acidic by sulfur dioxide gas dissolving in atmospheric water. It forms when fuels containing sulfur impurities are burned, and damages ecosystems and buildings.

Rising crude oil prices increase heating and travel costs for consumers, and also cause an indirect rise in food prices because oil is used to power food production and transport.

False.

Crude oil is also used to make products such as plastics and medicines, so there may be a future choice between burning reserves or preserving them for other uses.

War or conflict in oil-producing countries can result in oil supplies being cut off to other countries, causing shortages and economic disruption globally.

Crude oil is a finite resource, meaning that as demand increases, its price is expected to increase over time.

Complete combustion is a reaction in which a fuel burns in plenty of oxygen so that all elements in the fuel react fully. Hydrocarbon fuels produce carbon dioxide and water only.

When a hydrocarbon undergoes complete combustion, the carbon reacts with oxygen to form carbon dioxide and the hydrogen reacts with oxygen to form water.

False.

Combustion reactions are exothermic because they release energy to the surroundings.

CH₄ + 2O₂ → CO₂ + 2H₂O

Carbon dioxide and water are the only products of complete combustion of a hydrocarbon.

Balance the carbon atoms first, then the hydrogen atoms and finally the oxygen atoms.

Fuels are substances that react with oxygen to release energy in an exothermic process called combustion.

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

Balance carbon first (3), then hydrogen (8 ÷ 2 = 4 water molecules), then oxygen (6 + 4 = 10 atoms, so 5O₂).

False.

A hydrocarbon contains hydrogen and carbon atoms only. Including oxygen in the definition is incorrect.

Calorimetry is an experimental technique used to measure the energy released by a fuel. A fuel is burned beneath a known mass of water and the temperature change of the water is recorded.

The heat energy change is calculated using Q = m × c × ΔT, where c is the specific heat capacity of water (4.18 J/g/°C).

False.

The equation Q = mcΔT is provided. You only need to be able to use it to calculate energy released from given data.

Q = m × c × ΔT

Q = 200 × 4.18 × 30 = −25 080 J

The negative sign shows the reaction is exothermic.

Specific heat capacity is the energy needed to raise the temperature of 1 g of a substance by 1 °C. The specific heat capacity of water is 4.18 J/g/°C.

A lid is used to prevent heat loss to the surroundings, which would reduce the temperature rise recorded and lead to an underestimate of the energy released.

In a calorimetry experiment, the mass of fuel burned is found by measuring the mass of the spirit burner before and after burning.

False.

A negative value of Q indicates an exothermic reaction because it shows that energy was released to the surroundings.

Measure 100 cm³ of water into a conical flask. Record the initial temperature and mass of the spirit burner. Light the burner and heat the water until the temperature rises by ~40 °C. Record the final temperature and re-weigh the spirit burner. Repeat for each fuel.

Energy released per gram = (mass of water × temperature change × 4.2) ÷ mass of alcohol burned.

False.

The thermometer must not touch the bottom of the conical flask because this would give an inaccurate temperature reading.

The larger the alcohol molecule, the more energy it releases per gram. There is a positive relationship between molecule size and energy released per gram.

A spirit burner is a piece of apparatus used in combustion experiments that contains a liquid fuel (such as an alcohol). The fuel is burned under a container of water to measure the energy released.

In the energy from fuels practical, alcohols are highly flammable so the experiment must be conducted in a well ventilated laboratory away from other flames.

The difference in mass gives the mass of fuel burned, which is needed to calculate the energy released per gram of fuel.

False.

The equation for energy released per gram is provided. You only need to be able to apply it using the data from the experiment.

A hydrogen fuel cell is a device that uses a reaction between hydrogen and oxygen to generate electricity. Water is the only product, making it a clean energy source.

When hydrogen burns in oxygen, the only product formed is water, which means burning hydrogen does not contribute to global warming.

False.

Hydrogen is difficult and dangerous to store because it requires bulky pressurised containers and forms an explosive mixture with air.

2H₂ + O₂ → 2H₂O

The reaction is exothermic and produces water as the only product.

Advantage: Burning hydrogen produces only water, so it does not contribute to global warming or acid rain.

Disadvantage: Large amounts of electricity are needed to produce hydrogen by electrolysis, which may itself use fossil fuels.

True.

Hydrogen is produced by the electrolysis of water, though this process requires large amounts of electricity.

Hydrogen is described as a renewable fuel because the hydrogen is produced from water, which can be replenished.

Two applications of hydrogen as a fuel are:

1. Rocket engines

2. Fuel cells to power cars and buses

The fire triangle is a model showing the three factors needed for a fire to occur: fuel, heat and oxygen. Removing any one of the three factors will stop or prevent a fire.

A fire can be extinguished by removing any one side of the fire triangle: fuel, heat or oxygen.

False.

Water is not suitable for oil fires because it can cause the oil to form droplets, which increases the surface area and makes the fire burn more intensely.

A carbon dioxide extinguisher works by removing oxygen from around the fire. Once the oxygen is used up, the fire is extinguished because combustion cannot continue without it.

A fire break is a section of forest or moorland where all the fuel (trees and vegetation) has been cut down or removed. Without fuel, a fire cannot spread across the break.

True.

Opening a door to a fire provides it with fresh oxygen, which allows combustion to continue and the fire to intensify.

Water is not used on electrical fires because of the risk of electric shocks, and not on oil fires because it increases the surface area of the burning oil.

Two methods of removing fuel to prevent fire are:

1. Treating clothing and materials to make them fire-resistant

2. Building fire-proof compartments (walls, ceilings or fire doors) in modern buildings

Cracking is an industrial process that breaks long chain hydrocarbon molecules with low demand into shorter, more useful molecules by heating them to around 600–700 °C and passing the vapour over a hot powdered catalyst.

False.

Cracking converts long chain hydrocarbon molecules with low demand into shorter chain molecules that are more useful as fuels and raw materials.

Cracking produces a mixture of shorter alkanes (saturated) and alkenes (unsaturated) hydrocarbon molecules.

C₆H₁₄ → C₄H₁₀ + C₂H₄

Hexane (6C, 14H) produces butane (4C, 10H) and ethene (2C, 4H). The carbon and hydrogen atoms balance on each side.

Cracking is carried out because the demand for short chain fractions (such as petrol) is greater than the supply, while there is excess supply of long chain fractions with low demand.

During cracking, the hydrocarbon vapour passes over a hot powdered catalyst of alumina or silica, which causes catalytic cracking of the molecules.

True.

Alkenes such as ethene contain a reactive C=C double bond, which makes them useful as starting materials for addition polymerisation to produce plastics.

The other product is C₁₈H₃₈ (20 − 2 = 18 carbons; 42 − 4 = 38 hydrogens). It is an alkane because it follows the general formula C_nH_2n+2.

Add bromine water to the product. If it decolourises (turns from orange-brown to colourless), the substance is an alkene because the C=C double bond reacts with bromine in an addition reaction.

An alkane is a saturated hydrocarbon with the general formula C_nH_2n+2. All carbon-carbon bonds are single bonds. Examples include methane, ethane, propane and butane.

Alkenes are unsaturated hydrocarbons with the general formula C_nH_2n. They contain at least one carbon-carbon double bond.

True.

The suffix -ane indicates the molecule contains only single carbon-carbon bonds and is therefore saturated.

Pentane (alkane, C_nH_2n+2): C₅H₁₂

Pent-1-ene (alkene, C_nH_2n): C₅H₁₀

A functional group is the part of a molecule responsible for its characteristic reactions. In alkenes, the functional group is the C=C double bond, which allows them to react in ways that alkanes cannot.

A carbon-carbon double bond (C=C) requires two carbon atoms. A molecule with only one carbon atom cannot contain a C=C bond.

(Higher Tier Only)

A complex alkane with a methyl branch on carbon 3 of a 5-carbon chain is named 3-methylpentane.

False.

Side-chain numbers should give the lowest possible values. Always number the carbon chain so that branch positions have the smallest numbers.

This is a common naming error. The longest carbon chain is actually 5 carbons (pentane), so the molecule should be named 3-methylpentane, not 2-ethylpropane.

Isomers are compounds with the same molecular formula but a different structural formula. They contain the same type and number of atoms but arranged differently.

False.

Propane has no structural isomers because there is only one way to arrange 3 carbons and 8 hydrogens while satisfying all valencies.

(Higher Tier Only)

The first alkane that can form isomers has the molecular formula C₄H₁₀ and forms 2 different structural isomers (butane and 2-methylpropane).

C₅H₁₂ has 3 structural isomers:

1. Pentane

2. 2-methylbutane

3. 2,2-dimethylpropane

C₄H₈ has 3 structural isomers:

1. But-1-ene

2. But-2-ene

3. 2-methylpropene

(Higher Tier Only)

Isomers have the same molecular formula but different structural formulae.

False.

Neither ethene nor propene have structural isomers because there is only one way to arrange their atoms while satisfying all valencies.

Addition polymerisation is a reaction in which many small monomer molecules (containing a C=C double bond) join together to form a large polymer molecule. The C=C bond opens up and only single bonds remain in the polymer.

A monomer is a small, reactive molecule that contains a carbon-carbon double bond (C=C). Monomers can join together in addition polymerisation to form a polymer.

False.

In addition polymerisation, the C=C bonds in the monomers break open and join to adjacent molecules. The resulting polymer contains only single bonds.

To name a polymer, place the name of the monomer in brackets and add the prefix poly-. The exception is poly(ethene), which is called polythene.

The polymer formed from vinylchloride monomers is poly(vinylchloride), also known as PVC.

The lower case n represents the number of monomer molecules involved. It indicates there are many monomers joining together to form the polymer.

In addition polymerisation equations, single continuation bonds are drawn continuing outside the brackets on each carbon to show that the chain extends further.

True.

Poly(tetrafluoroethene) (also known as PTFE) is used to coat non-stick pans because of its very low friction and heat resistance.

An addition reaction is a reaction in which atoms of a simple molecule add across the C=C double bond of an alkene, forming a saturated compound with only single bonds.

False.

Alkenes decolourise bromine water because bromine adds across the C=C double bond. Alkanes have no double bond and so bromine water stays orange.

When bromine water is added to an alkene, the solution changes from orange to colourless as bromine adds across the C=C bond.

CH₂CH₂ + H₂ → CH₃CH₃

Hydrogen adds across the C=C bond of ethene to produce ethane, a saturated alkane.

Hydrogenation is used to manufacture margarine from vegetable oils. The vegetable oils are polyunsaturated and are partially hydrogenated to increase their M_r and turn them into solid fats.

In the bromine water test, a saturated alkane keeps the solution orange because it has no double bond for the bromine to add across.

True.

All alkenes contain the C=C functional group, which means they all undergo similar addition reactions regardless of chain length.

CH₂CH₂ + Br₂ → CH₂BrCH₂Br

Bromine atoms add across the C=C bond to produce a bromoalkane.

A non-biodegradable material is one that cannot be broken down by micro-organisms such as decomposers. Most plastics are non-biodegradable, meaning they persist in the environment for hundreds of years.

Poly(vinylchloride) is used to insulate electrical wiring because it is a very good insulator, which helps prevent electric shocks and overheating.

False.

Burning (incineration) of plastics produces the greenhouse gas carbon dioxide and some plastics also release toxic fumes (e.g. poly(vinylchloride) releases hydrogen chloride gas).

Three general properties of plastics are:

1. Flexible and strong

2. Good thermal and electrical insulators

3. Resistant to corrosion and non-biodegradable

Plastics are non-biodegradable, so micro-organisms cannot break them down. Plastic items will remain in landfill sites for hundreds of years, causing sites to fill up rapidly and take up valuable land.

Recycling plastic helps to conserve crude oil reserves because less energy is required to recycle plastics than to produce them from raw materials.

False.

Poly(tetrafluoroethene) (PTFE) is used to make non-stick pans. Poly(propene) is used to make ropes and crates.

A choice may have to be made between burning remaining oil reserves for energy or preserving them as raw materials for plastics and medicines. Both uses are important to modern society.