Comparing Energy Resources

Understanding how we obtain and use energy is a key part of the AQA GCSE Chemistry specification. This lesson compares different energy resources — fossil fuels, hydrogen, batteries, and fuel cells — in terms of their energy output, environmental impact, sustainability, and practicality. You will learn to evaluate these resources and make informed judgements.

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Types of Energy Resources

Energy resources can be broadly divided into non-renewable and renewable categories:

Category	Examples	Key Feature
Non-renewable	Coal, oil, natural gas, nuclear	Finite supply — will eventually run out
Renewable	Wind, solar, hydroelectric, tidal, geothermal, biomass	Continuously replenished — will not run out

In GCSE Chemistry, the focus is on how chemical reactions provide energy, so we concentrate on fossil fuels, hydrogen, and electrochemical cells (batteries and fuel cells).

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Fossil Fuels

Fossil fuels (coal, oil, and natural gas) are formed from the remains of ancient organisms over millions of years. They are burned (combustion) to release energy.

Combustion of Fossil Fuels

When fossil fuels undergo complete combustion in excess oxygen:

hydrocarbon + oxygen --> carbon dioxide + water

When there is incomplete combustion (limited oxygen supply):

hydrocarbon + oxygen --> carbon monoxide + water (and sometimes carbon/soot)

Fuel	Chemical Formula	Energy Released (kJ/g)	Products of Complete Combustion
Methane (natural gas)	CH4	~55	CO2 + H2O
Propane	C3H8	~50	CO2 + H2O
Octane (petrol)	C8H18	~48	CO2 + H2O
Coal (mainly carbon)	C	~33	CO2
Hydrogen	H2	~142	H2O only

Exam Tip: Hydrogen has the highest energy content per gram of any fuel AND produces only water when burned. However, it is not a fossil fuel — it must be manufactured, which itself requires energy.

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Environmental Impact of Fossil Fuels

Pollutant	Source	Environmental Effect
Carbon dioxide (CO2)	Complete combustion of any carbon-containing fuel	Greenhouse gas — contributes to global warming and climate change
Carbon monoxide (CO)	Incomplete combustion	Toxic gas — binds to haemoglobin, preventing oxygen transport
Sulfur dioxide (SO2)	Combustion of fuels containing sulfur impurities	Causes acid rain — damages buildings, ecosystems, and waterways
Nitrogen oxides (NOx)	High-temperature combustion in car engines	Causes acid rain and contributes to smog; respiratory irritant
Particulates (soot)	Incomplete combustion	Causes respiratory diseases; contributes to global dimming
Unburned hydrocarbons	Incomplete combustion	Contribute to smog; some are carcinogenic

graph TD
    A["Burning Fossil Fuels"] --> B["CO2 - Greenhouse Effect"]
    A --> C["CO - Toxic Gas"]
    A --> D["SO2 - Acid Rain"]
    A --> E["NOx - Acid Rain and Smog"]
    A --> F["Particulates - Health Problems"]
    B --> G["Global Warming and Climate Change"]
    D --> H["Damage to Buildings and Ecosystems"]
    E --> H
    F --> I["Respiratory Disease"]

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Hydrogen as a Fuel

Hydrogen can be used as a fuel in two ways:

1. Combustion — burning hydrogen in oxygen: 2H2 + O2 --> 2H2O
2. Fuel cells — hydrogen reacts with oxygen in a fuel cell to produce electricity and water.

Feature	Hydrogen Combustion	Hydrogen Fuel Cell
Product	Water	Water
Efficiency	Lower (energy lost as heat)	Higher (direct conversion to electricity)
Emissions	Water only (no CO2)	Water only (no CO2)
Use	Rockets, some vehicles	Vehicles, portable power, spacecraft

The Challenge of Hydrogen Production

Method	Description	Carbon Footprint
Steam reforming	Reacting methane with steam at high temperature (CH4 + H2O --> CO + 3H2)	High — produces CO2
Electrolysis of water	Using electricity to split water into H2 and O2	Depends on electricity source — zero if renewable

Exam Tip: When evaluating hydrogen as a fuel, always consider HOW the hydrogen is produced. If it comes from steam reforming of natural gas, it is NOT truly carbon-neutral because CO2 is produced in the manufacturing process.

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Comparing Chemical Cells, Batteries, and Fuel Cells

Feature	Non-Rechargeable Cell	Rechargeable Battery	Hydrogen Fuel Cell
Energy source	Chemicals sealed inside	Chemicals sealed inside (reversible)	External hydrogen fuel supply
Lifetime	Stops when chemicals used up	Limited charge-discharge cycles	Continuous (as long as fuel supplied)
Waste	Must be disposed/recycled	Must eventually be disposed/recycled	Water only
Portability	Excellent	Excellent	Requires fuel storage tank
Cost	Low	Medium	High
Environmental impact	Heavy metals, landfill issues	Heavy metals, but less waste over time	Clean at point of use; depends on H2 production

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Evaluating Energy Resources — A Framework

When evaluating energy resources in an exam, consider these factors:

Factor	Questions to Ask
Availability	Is the resource readily available? Will it run out?
Cost	How much does it cost to extract, process, and use?
Environmental impact	What pollutants are produced? Does it contribute to climate change?
Efficiency	How much of the stored energy is converted to useful energy?
Reliability	Is the supply constant, or does it depend on weather/conditions?
Safety	Are there risks in storage, transport, or use?
Infrastructure	Is the necessary infrastructure (e.g., refuelling stations) in place?
Sustainability	Can this resource be used indefinitely without depleting it?

Exam Tip: In an evaluation question (typically worth 6 marks), you must consider MULTIPLE factors and reach a justified conclusion. A good answer discusses at least 3-4 factors, provides specific examples, and gives a balanced conclusion that acknowledges both sides.

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The Future of Energy

The global energy landscape is shifting from fossil fuels towards cleaner alternatives. Key trends include:

Trend	Detail
Electric vehicles (EVs)	Powered by rechargeable lithium-ion batteries; zero emissions at point of use
Hydrogen fuel cell vehicles	Zero emissions at point of use; rapid refuelling; limited infrastructure
Renewable electricity	Wind, solar, and tidal power generating increasing proportions of electricity
Energy storage	Better batteries and hydrogen storage needed to balance intermittent renewable supply
Carbon capture	Technologies to capture CO2 from power stations before it enters the atmosphere