Resources of Materials & Energy (AQA GCSE Combined Science: Synergy: Physical Sciences): Flashcards

In the electrolysis of aluminium oxide, aluminium metal is produced at the cathode and oxygen gas is produced at the anode.

Oxygen produced at the anode reacts with the carbon (graphite) in the anodes to form CO₂:

C (s) + O₂ (g) → CO₂ (g)

This gradually burns away the anodes, which must be replaced to maintain the electrolysis.

Electrolysis requires large amounts of electrical energy — both to melt the ionic compound (so ions can move freely) and to drive the electrolysis process. Carbon reduction uses carbon as a cheap fuel and reducing agent, making it much less expensive.

False.

Cryolite is used because it lowers the melting point of the aluminium oxide mixture, reducing the energy needed to keep it molten. Cryolite does not interfere with the reaction or supply aluminium ions.

Phytomining is a biological method of extracting metals. Plants grown in soil containing metals absorb metal compounds through their roots. The plants are harvested, dried, and burned; the ash contains metal compounds that can be processed to obtain the metal.

Bioleaching is a biological method of extracting metals using bacteria. The bacteria break down metal ores to produce an acidic leachate solution containing metal compounds, which is then processed to obtain the metal.

False.

Both phytomining and bioleaching are actually very slow methods. They are used primarily because high-grade copper ores are becoming scarce, allowing extraction from low-grade ores that would be uneconomical by traditional methods.

1. Less CO₂ and SO₂ emissions — traditional mining burns fossil fuels, contributing to global warming and acid rain; biological methods produce far fewer emissions

2. Less habitat destruction — biological methods avoid large-scale excavation, preserving wildlife habitats and reducing landscape damage

Copper can be obtained from bioleaching leachate by displacement using scrap iron, or by electrolysis of the solution.

Iron is more reactive than copper, so it displaces copper from solution:

Fe (s) + CuSO₄ (aq) → FeSO₄ (aq) + Cu (s)

A pink/brown copper solid is deposited and the blue colour of the solution fades.

False.

Bioleaching produces toxic substances in the leachate that must be carefully treated to prevent environmental contamination. This is a key disadvantage compared to some other extraction methods.

A non-renewable energy resource is one that is used up faster than it can be replenished and will eventually run out. Examples include fossil fuels (coal, crude oil, natural gas) and nuclear fuel.

A renewable energy resource is one that is being (or can be) replenished as it is used, so it will not run out. Examples include wind, solar, hydroelectric, tidal, and biofuels.

False.

Wind and solar energy depend on weather conditions — they generate electricity only when it is windy or sunny respectively. Fossil fuel power stations must be kept available as backup for when renewable sources are insufficient.

1. Burning fossil fuels releases CO₂, a greenhouse gas that contributes to global warming

2. Burning fossil fuels also releases SO₂, which causes acid rain

(Also: particulates are released, which affect health and cause global dimming)

Fossil fuels generate electricity by burning the fuel to heat water, which turns turbines, connected to generators that produce electricity.

Water is stored at a height in a reservoir. When released, it flows downhill, converting gravitational potential energy to kinetic energy. The rushing water turns turbines connected to generators, producing electricity.

False.

Electric vehicles produce zero emissions while being driven, but the electricity used for charging may still come partly from non-renewable sources. The overall emissions depend on how the electricity is generated.

Wind turbines: noise pollution, visual pollution, and risk to birds.

Hydroelectric: habitat disruption caused by flooding valleys to create reservoirs.

The law of conservation of energy states that energy cannot be created or destroyed — it can only be transferred from one store to another. The total energy in a closed system remains constant.

Dissipation is the spreading out of energy to the thermal store of the surroundings in a less useful form. Dissipated energy is considered wasted because it is no longer available for the intended purpose.

False.

Energy is never destroyed. "Wasted" energy is dissipated — it is transferred to the thermal store of the surroundings in a less useful form. The total amount of energy is always conserved.

Useful transfer: energy from the bat’s kinetic store transfers to the ball’s kinetic store.

Wasted transfers: energy is dissipated to the thermal stores of the bat, ball, and surroundings through heating and sound.

On a rollercoaster descending a hill, energy transfers from the gravitational potential store to the kinetic store. At the bottom, the rollercoaster speeds up. Some energy is always dissipated to the surroundings.

Wasted energy is energy that is not used for the intended purpose and is dissipated to the surroundings — usually as heat or sound. It is stored in the thermal store of the surroundings in a less useful, spread-out form.

False.

An electric heater transfers most energy to the thermal store of the surroundings by heating, which is useful. However, some energy is also dissipated as light (radiation), which is wasted energy not intended for heating the room.

Lubrication reduces friction between surfaces that rub together, decreasing the amount of energy dissipated as heat. This increases the efficiency of machines by reducing unwanted energy transfers.

Thermal conductivity is a property of a material describing how quickly energy is transferred by conduction through it. Insulation materials have low thermal conductivity, slowing unwanted energy loss.

True.

Thicker walls mean energy must conduct through a greater depth of material, which takes longer. This reduces the rate of cooling of the building, so less energy is needed to maintain the desired temperature.

Lubrication reduces friction between moving surfaces. Without lubrication, work is done against friction, causing a rise in temperature and dissipating useful energy to the surroundings as heat. Lubricants allow surfaces to slide more easily, reducing this wasted energy transfer.

The rate of energy loss through a wall depends on the thickness of the wall and the thermal conductivity of the material. A material with low thermal conductivity is a better insulator.

1. Lubrication — reduces friction between moving parts in machines, reducing energy dissipated as heat

2. Thermal insulation — surrounds objects or buildings with insulating material to reduce energy transfer by conduction to the surroundings

False.

A material with high thermal conductivity allows energy to transfer quickly by conduction, which would make energy loss faster. Good insulation materials have low thermal conductivity to slow the rate of energy transfer.

Efficiency is the ratio of useful output energy (or power) to total input energy (or power). It shows what fraction of the input energy is transferred usefully, and can be expressed as a decimal or percentage.

efficiency = useful output energy transfer ÷ total input energy transfer

Alternatively, using power:

efficiency = useful power output ÷ total power input

Efficiency has no units and is between 0 and 1 (or 0% and 100%).

True.

An efficiency of 0.75 (or 75%) means that 75% of the total input energy is transferred usefully for the intended purpose. The remaining 25% is dissipated to the surroundings as wasted energy.

A system with low efficiency wastes most of its input energy. A system with high efficiency transfers most of its input energy usefully.

efficiency = useful output energy ÷ total input energy

efficiency = 350 ÷ 500 = 0.7

As a percentage: 0.7 × 100 = 70%

The remaining 30% is dissipated as wasted energy.

False.

Efficiency can never exceed 1 (or 100%) because that would mean creating energy, violating the law of conservation of energy. All real devices waste some energy, so efficiency is always less than 1.

1. Lubrication — reduces friction between moving parts, so less energy is dissipated as heat

2. Thermal insulation — reduces energy loss by conduction to the surroundings, so less energy is wasted

A life cycle assessment (LCA) is an analysis of the overall environmental impact of a product throughout its entire lifetime, from raw material extraction to final disposal.

1. Extracting and processing raw materials

2. Manufacturing and packaging

3. Use and operation during its lifetime

4. Disposal at the end of its useful life

Transport and distribution is also considered at each stage.

False.

Some aspects (e.g. water usage, waste quantity) can be easily quantified. However, allocating numerical values to pollutant effects requires value judgements and is not fully objective. This means LCAs can be manipulated to reach pre-determined conclusions.

A plastic shopping bag is reusable and does not biodegrade, but is not easily recycled and takes up space in landfill.

Companies may use abbreviated or selective LCAs that highlight environmental benefits while ignoring negative impacts. This allows them to make misleading environmental claims in advertising without presenting the complete picture of a product’s environmental impact.

Paper bag: biodegradable and non-toxic; can be recycled easily.

Plastic bag: not biodegradable; takes up space in landfill; can be recycled but this is costly and produces pollution.

False.

It depends on usage. Pulping paper uses a lot of energy and produces SO₂ and waste. If the plastic bag is reused many times, it may have a lower overall impact. If the paper bag is recycled, it becomes more favourable. There is no single correct answer — the LCA depends on specific circumstances.

1. Less mining is required, reducing habitat destruction and landscape damage

2. Less energy is needed for recycling than for extraction, so fewer CO₂ emissions and less contribution to global warming

True.

Glass bottles can be washed and sterilised before being reused directly. This is more energy-efficient than recycling (which requires crushing and remelting) and reduces the use of raw materials and waste production.

Recycling is the process of collecting and reprocessing waste materials (such as metals, glass, and plastics) to produce new products. It reduces the use of limited raw materials, saves energy, and reduces waste sent to landfill.

Recycling metals involves melting and recasting them into new products. Scrap steel can be added to iron from a blast furnace to reduce the amount of iron that needs to be extracted from ore.

1. Collection, transport, and sorting of materials requires energy and labour, adding cost and emissions

2. Products made from recycled materials may not always be of the same quality as those made from virgin raw materials

True.

Recycling reduces the demand for finite raw materials such as metal ores and crude oil. As global populations grow, recycling is increasingly important for achieving sustainable development — meeting present needs without compromising future generations.

Extracting aluminium from bauxite by electrolysis requires very large amounts of electrical energy, making it very expensive. Recycling aluminium requires far less energy (just melting and remoulding), making it much more cost-effective and reducing CO₂ emissions.